STRENGTHENING R/C COLUMNS BY JACKETING using …library.iugaza.edu.ps/thesis/112842.pdf · m.sc....

M.SC. THESIS

STRENGTHENING OF SQUARE REINFORCED CONCRETE COLUMNS

WITH FIBROUS ULTRA HIGH PERFORMANCE SELF-COMPACTING

CONCRETE JACKETING

داء، ذاتية الدمك عمدة الخرسانية المسلحة مربعة المقطع بعمل قمصان مصنعة من خرسانة عالية األتقوية األ

بروبلينلياف البوليومدعمة بأ

Researcher

ZAKARIA H. HELLES

Supervisors

DR. MOHAMMED ARAFA DR. MAMOUN ALQEDRA

A Thesis Submitted in Partial Fulfillment of the Requirements for the Master

Degree in Design and Rehabilitation of Structures at the Islamic University

Gaza

MARCH, 2014

The Islamic University Gaza

Higher Education Deanship

Faculty of Engineering

Civil Engineering Department

Design and Rehabilitation of

Structures

الجـــــــامعة االســـــالمية بـغزة

عمادة الدراســـــات العليــــــــــا

كليــــــــــــــــة الهندســـــــــــــة

قســـــم الهندســـــــة المدنيـــــة

تآبرنامج تصميم وتأهيل المنشـ

II

ABSTRACT

In recent years, researches have been increasing towards studying the strengthening of

concrete structures using different methods. Various studies have shown that structural

concrete members such as square reinforced concrete (RC) columns can experience a

significant increase in the ultimate load carrying capacity and ductility when

strengthened by a concrete jacket. Despite the large number of performed studies, most

of them did not consider the application of fibrous ultra high performance self-

compacting concrete as a jacketing material. This study aimed at investigating the

effectiveness of strengthening the entire height of downscaled square RC columns by

applying Forta Ferro Polypropylene Fibrous Ultra High Performance Self Compacting

Concrete (Fibrous UHPSCC) as a jacketing material.

The experimental work included the fabrication of three identical unjacketed reference

columns (UC) having similar cross sections of 100×100mm and 300mm high. Nine

monolithically cast reference columns (MC) were fabricated having three cross

sections of 150×150, 160×160, 170×170 mm and 300mm high. The UC and MC

reference columns were made of normal strength concrete (NSC). A total of 27 identical

column cores were made of NSC having similar cross sections of 100×100mm and

300mm high. The four sides of the 27 column cores were strengthened by applying

three jacketing styles with three jacket thicknesses namely; 25, 30 and 35 mm.

The applied three jacketing styles in this study were; Group1 (G1) consisted of nine

column cores jacketed by Fibrous UHPSCC without steel reinforcement, Group2 (G2)

consisted of nine column cores jacketed by Non-Fibrous UHPSCC with steel

reinforcement, and Group3 (G3) consisted of nine column cores jacketed by Fibrous

UHPSCC with steel reinforcement. All the fabricated column specimens were tested

under monotonic uniaxial compression loading in order to investigate the ultimate load

carrying capacity, longitudinal axial strain and failure pattern.

A comparative study was performed between the jacketed column specimens and the

reference columns. The G1, G2 and G3 jacketed column specimens showed significant

increase in the ultimate load carrying capacity higher about 4.4 times than the UC

reference column, and higher about 2.1 times than the MC reference columns

respectively. The measured longitudinal axial strain of G1 and G3 jacketed column

specimens was higher about 2.1 and 2.3 times than that of UC and MC reference

columns respectively. Whereas the longitudinal axial strain of G2 jacketed column

specimens was reduced by about 27% less than that of UC and MC reference columns.

The results also revealed that the failure patterns and crack formation were significantly

influenced by both the jacketing thickness and the jacketing style.

III

ARABIC ABSTRACT ثظشأ. لذ سخخذا طشق عذةإب اخشسايت اشآث صالحإ حميت خيشةفي اآلت األاذساساث حاج اعذيذ

لة صادث والخشسايت لذ امصا ابعذة اخشسايت شبعت امطع أ حميت األاعذيذ ز اذساساث

أجشيج عى اخي ثذساسا اعذد اىبيشاشغ عى طيخا عى اساء. سيتأداي اشأل عذةحذ األ

سن األ عذة اخشسايت ا عذة اخشسايت بع حميت األ عخباسحضع في األ ز اذسساث غبأفإ ،تيم

بي.شياف ابيباألداء، راحيت اذه ذعت بؤخشسات عايت لصا صعت

عياث اىي طيابخغيف شبعت امطعا اسذت عذة اخشسايتحميت األوفاءة دساست ابذث از حايديث

.ابيبشبيياف ؤداء، راحيت اذه ذعت بشسايت صعت خشسات عايت األخ مصابعذة األ

تشبع تسذ( غيش ميت تشجعيعذة أ) (UC)تخشساي ةعذأ ثالثتصب عى اعيت اذساست شخجإ لذ

ح صبا وىخت شجعيتعذة أ) (MC) عذة خشسايتأ، صب حسعت 011اسحفاع ب 011×011امطع

أسخخذج اخشسات . 011سحفاع إب 071×071، 011×011، 011×011 ( سذت شبعت امطعادذة

. UC MC اشجعيتاعاديت صب جيع األعذة اخشسايت

011×011عد خشساي سخ شبع امطع 77صب ا جع أسخخذج اخشسات اعاديت في وا

خشسايت امصا ا حطبيك ثالثت حمياث ع ع طشيك جاب األسبعت حغيف، ره بغشض 011سحفاع إب

.01، 01، 71 ي ساواثبثالثت

اخي ح G1ى األاألعذة خالي ز اذساست ي جعتمذ ح حطبيك ثالثت حمياث ع امصا اخشسايت

ضافت دذيذ إياف ابيبشبي ع عذ صا خشسايت خشسات عايت األداء ذعت بؤعذحا بع لأحميت

صا خشسايت خشسات عذحا بع لأاخي ح حميت G2اثايت األعذة جعت حسيخ ميص اخشساي،

اثاثت األعذة جعت ضافت دذيذ حسيخ ميص اخشساي، عايت األداء غيش ذعت بؤياف ابيبشبي ع إ

G3 ضافت داء ذعت بؤياف ابيبشبي ع إيت خشسات عايت األعذحا بع لصا خشساأاخي ح حميت

دذيذ حسيخ ميص اخشساي.

ره عى شوض اعد خساجضغظ سأسي د بخطبيك في اخخبش اخشسايتاألعذة عياث فذص جيع ح

حجا اخذي إفي األعذة يت طسيت، أداي اشذ األح فياألعذة بمةبذف اذصي عى اخائج اخعمت

طبيعت شى االياس.

ظشث أديث اشجعيت.األعذة خائج ع عذة اميتأل اعيت اخي ح اذصي عيا خائج ماست جشيجأث

ضعاف أ 4.4 حعادي وسش اعدلذ دصج عى صيادة وبيشة في لة G1 ،G2 G3جعاث ا عذةأ أاخائج

UCاشجعيت األعذة لة وسش G1 ،G2 G3 عذة اجعاثأوا واج اضيادة في لة وسش . ميتاغيش

اخي ح صبا وىخت ادذة.MC اشجعيتاألعذة لة وسشضعف 2.1حعادي

ضغاطإلاألعذة حذ لذسة ا صاد G1 G3 اجعخي عذةأ صيادة ذظت في طيت ججوا س

عى UC MC اشجعيتاألعذة طيت ضعاف أ 7.0 7 يعاديواج اضيادة في اطيت با سيأشا

اشجعيت.األعذة طيت % 77 مذاسب لأ G2 تجععذة اأطيت ج ، في دي وااخاي

امصا اخشسايت ساوت ى بثيشا وبيشا ؤحيخاثشا اخشمماث طبيعتياس أ شى اإليضا أظشث اخائج ألذ

يت اسخخذت في اخميت.اآلوزه

IV

DEDICATION

I would like to dedicate this work to my family specially my mother who loved and

raised me and to the soul of my father who wished me this success, to my loving wife

and daughter and to my brothers and sisters, for their sacrifice and endless support and

to whom I belong.

V

ACKNOWLEDGMENT

I would like to express my sincere appreciation to Dr. Mohammed Arafa and Dr.

Mamoun Alqedra from the Department of Civil Engineering at The Islamic University

of Gaza, for their help, guidance and assistance in all stages of this research. The

constant encouragement, support and inspiration they offered were fundamental to the

completion of this research.

Special thanks go to the Material and Soil Laboratory of the Islamic University-Gaza,

for their logistic facilitations and their continuous support as well as to all my lecturers

from whom I learned much and developed my skills.

I would like to express my deep thanks for my brothers and friends for their assistance

during the practical work of the research.

Finally I would like to thank everyone who gave advice or assistance that contributed to

complete this research.

VI

TABLE OF CONTENTS

ABSTRACT ----------------------------------------------------------------------------------------------------------- II

ARABIC ABSTRACT --------------------------------------------------------------------------------------------- III

DEDICATION ------------------------------------------------------------------------------------------------------- IV

ACKNOWLEDGMENT -------------------------------------------------------------------------------------------- V

TABLE OF CONTENTS ------------------------------------------------------------------------------------------ VI

LIST OF TABLES -------------------------------------------------------------------------------------------------- IX

LIST OF FIGURES ------------------------------------------------------------------------------------------------- X

NOTATIONS ------------------------------------------------------------------------------------------------------- XII

INTRODUCTION --------------------------------------------------------------------------------- 1 CHAPTER 1 -

1.1. INTRODUCTION ----------------------------------------------------------------------------------------------------- 2

1.2. PROBLEM STATEMENT --------------------------------------------------------------------------------------------- 3

1.3. RESEARCH OBJECTIVES ------------------------------------------------------------------------------------------- 4

1.4. METHODOLOGY ---------------------------------------------------------------------------------------------------- 4

1.5. THESIS LAYOUT ---------------------------------------------------------------------------------------------------- 5

LITERATURE REVIEW ------------------------------------------------------------------------ 7 CHAPTER 2 -

2.1. INTRODUCTION ----------------------------------------------------------------------------------------------------- 8

2.2. STRENGTHENING TECHNIQUES OF RC COLUMNS ------------------------------------------------------------- 8

Jacketing RC Columns using Steel Profile -------------------------------------------------------------- 8 2.2.1.

Jacketing RC Columns by External Steel Battens Welded to Steel Angles ------------------------ 9 2.2.2.

Jacketing RC Columns by FRP -------------------------------------------------------------------------- 11 2.2.3.

Strengthening RC Columns by Concrete Jacketing -------------------------------------------------- 13 2.2.4.

2.3. FIBROUS ULTRA HIGH PERFORMANCE SELF-COMPACTING CONCRETE --------------------------------- 22

Ultra-High Performance Concrete (UHPC) ------------------------------------------------------------ 22 2.3.1.

Self-Compacting Concrete (SCC) ----------------------------------------------------------------------- 22 2.3.2.

The Developing History of UHPSCC------------------------------------------------------------------ 23 2.3.3.

Types of Fibers -------------------------------------------------------------------------------------------- 23 2.3.4.

Polypropylene Fibers ------------------------------------------------------------------------------------------- 24 2.3.4.1.

Forta Ferro Polypropylene Fibers ----------------------------------------------------------------------------- 25 2.3.4.2.

2.4. PROPERTIES OF FIBROUS UHPSCC ---------------------------------------------------------------------------- 25

Strength ------------------------------------------------------------------------------------------------------ 25 2.4.1.

Durability ---------------------------------------------------------------------------------------------------- 26 2.4.2.

Workability ------------------------------------------------------------------------------------------------- 26 2.4.3.

Sustainability ----------------------------------------------------------------------------------------------- 27 2.4.4.

Affordability ------------------------------------------------------------------------------------------------ 27 2.4.5.

2.5. SUMMARY OF LITERATURE REVIEW -------------------------------------------------------------------------- 27

EXPERIMENTAL WORK -------------------------------------------------------------------- 29 CHAPTER 3 -

3.1. INTRODUCTION --------------------------------------------------------------------------------------------------- 30

3.2. EXPERIMENTAL PROGRAM -------------------------------------------------------------------------------------- 30

3.3. CATEGORIZING THE COLUMN SPECIMENS ------------------------------------------------------------------- 31

3.4. TYPES OF CONCRETE MIXES ------------------------------------------------------------------------------------ 33

3.5. PREPARATION OF UC, MC REFERENCE COLUMNS AND COLUMN CORES -------------------------------- 33

Properties of NSC Ingredients --------------------------------------------------------------------------- 33 3.5.1.

NSC Mixing Proportions --------------------------------------------------------------------------------- 34 3.5.2.

VII

Properties of Reinforcement Steel ---------------------------------------------------------------------- 34 3.5.3.

Reinforcement Details ------------------------------------------------------------------------------------- 35 3.5.4.

Mixing Procedures ----------------------------------------------------------------------------------------- 35 3.5.5.

Casting of NSC --------------------------------------------------------------------------------------------- 36 3.5.6.

Curing of NSC----------------------------------------------------------------------------------------------- 37 3.5.7.

3.6. PREPARATION OF THE JACKET ---------------------------------------------------------------------------------- 37

Properties of Fibrous UHPSCC -------------------------------------------------------------------------- 37 3.6.1.

Aggregates ------------------------------------------------------------------------------------------------------- 37 3.6.1.1.

Cement ----------------------------------------------------------------------------------------------------------- 38 3.6.1.2.

Mixing Water ---------------------------------------------------------------------------------------------------- 38 3.6.1.3.

Forta-Ferro Polypropylene Fibers (FFP) --------------------------------------------------------------------- 39 3.6.1.4.

Superplasticizer ------------------------------------------------------------------------------------------------- 39 3.6.1.5.

Silica Fume------------------------------------------------------------------------------------------------------- 40 3.6.1.6.

Mixing Proportions of Fibrous and Non-Fibrous UHPSCC ---------------------------------------- 41 3.6.2.

Reinforcement Details ------------------------------------------------------------------------------------- 41 3.6.3.

Mixing Procedures ----------------------------------------------------------------------------------------- 43 3.6.4.

Casting of UHPSCC --------------------------------------------------------------------------------------- 43 3.6.5.

Curing of UHPSCC ------------------------------------------------------------------------------------------ 44 3.6.6.

3.7. TESTING OF COLUMN SPECIMENS------------------------------------------------------------------------------ 44

The Ultimate Load Carrying Capacity of Column Specimens ------------------------------------- 45 3.7.1.

The Longitudinal Axial Strain of Column Specimens ----------------------------------------------- 45 3.7.2.

RESULTS & DISCUSSION ------------------------------------------------------------------- 46 CHAPTER 4 -

4.1. INTRODUCTION --------------------------------------------------------------------------------------------------- 47

4.2. NSC COMPRESSIVE STRENGTH -------------------------------------------------------------------------------- 47

4.3. UHPSCC COMPRESSIVE STRENGTH -------------------------------------------------------------------------- 47

4.4. UC REFERENCE COLUMN --------------------------------------------------------------------------------------- 48

Results of UC Ultimate Load Carrying Capacity ----------------------------------------------------- 48 4.4.1.

Results of UC Longitudinal Axial Strain -------------------------------------------------------------- 48 4.4.2.

4.5. MC REFERENCE COLUMNS ------------------------------------------------------------------------------------- 49

Results of MC Ultimate Load Carrying Capacity ---------------------------------------------------- 49 4.5.1.

Results of MC Longitudinal Axial Strain -------------------------------------------------------------- 51 4.5.2.

4.6. G1 JACKETED COLUMN SPECIMENS --------------------------------------------------------------------------- 53

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Ultimate Load Carrying Capacity4.6.1.

------------------------------------------------------------------------------------------------------------------------ 53

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Longitudinal Axial Strain -------- 56 4.6.2.

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Failure Pattern --------------------- 59 4.6.3.


Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 Ultimate Load Carrying 4.7.1.

Capacity ------------------------------------------------------------------------------------------------------------- 61

Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 Longitudinal Axial Strain4.7.2.

------------------------------------------------------------------------------------------------------------------------ 63

Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 Failure Pattern ----------- 67 4.7.3.


Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Ultimate Load Carrying 4.8.1.

Capacity ------------------------------------------------------------------------------------------------------------- 68

Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Longitudinal Axial Strain ---- 70 4.8.2.

Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Failure Pattern ----------------- 74 4.8.3.

4.9. ULTIMATE LOAD CARRYING CAPACITY AND AXIAL STRAIN OF G1, G2 AND G3 COLUMNS WITH

RESPECT TO UC AND MC -------------------------------------------------------------------------------------------- 74

CONCLUSIONS & RECOMMENDATIONS --------------------------------------------- 78 CHAPTER 5 -

5.1. INTRODUCTION --------------------------------------------------------------------------------------------------- 79

VIII

5.2. CONCLUSION ------------------------------------------------------------------------------------------------------ 79

5.3. RECOMMENDATIONS --------------------------------------------------------------------------------------------- 81

Findings ------------------------------------------------------------------------------------------------------ 81 5.3.1.

Suggestions ------------------------------------------------------------------------------------------------- 81 5.3.2.

REFERENCES ------------------------------------------------------------------------------------------------------ 82

INDEX ---------------------------------------------------------------------------------------------------------------- 87

IX

LIST OF TABLES

TABLE ‎2-1: UHPSCC DEVELOPMENT.‎[32] --------------------------------------------------------------------------- 23

TABLE ‎2-2: PHYSICAL PROPERTIES OF FORTA FERRO POLYPROPYLENE FIBERS.‎[4] --------------------------- 25

TABLE ‎2-3: EFNARC CRITERIA OF SELF-COMPACTING CONCRETE --------------------------------------------- 26

TABLE ‎3-1: DETAILS OF COLUMN SPECIMENS. ----------------------------------------------------------------------- 33

TABLE ‎3-2: NSC MIXING PROPORTIONS.‎[38] ------------------------------------------------------------------------ 34

TABLE ‎3-3: STEEL REINFORCEMENT TESTING RESULTS. ----------------------------------------------------------- 35

TABLE ‎3-4: CEMENT PROPERTIES BASED ON MANUFACTURER SHEET. [37] ------------------------------------ 38

TABLE ‎3-5: PHYSICAL PROPERTIES OF FORTA FERRO POLYPROPYLENE FIBERS.‎[4] --------------------------- 39

TABLE ‎3-6: SIKAMENT 163M TECHNICAL DATA.‎[37] -------------------------------------------------------------- 39

TABLE ‎3-7: SELF-COMPACTING PROPERTIES OF UHPSCC MIX. -------------------------------------------------- 40

TABLE ‎3-8: SIKA-FUME PROPERTIES.‎[37] ----------------------------------------------------------------------------- 40

TABLE ‎3-9: MIXING PROPORTIONS OF FIBROUS UHPSCC.‎[35] --------------------------------------------------- 41

TABLE ‎3-10: DETAILS OF G1, G2 AND G3 JACKETED COLUMN SPECIMENS. ------------------------------------ 41

TABLE ‎4-1: COMPRESSION TEST RESULTS OF NSC. ----------------------------------------------------------------- 47

TABLE ‎4-2: COMPRESSION TEST RESULTS OF FIBROUS AND NON-FIBROUS UHPSCC. ----------------------- 47

TABLE ‎4-3: UC ULTIMATE LOAD CARRYING CAPACITY. ---------------------------------------------------------- 48

TABLE ‎4-4: MC ULTIMATE LOAD CARRYING CAPACITY. ---------------------------------------------------------- 50

TABLE ‎4-5: G1 ULTIMATE LOAD CARRYING CAPACITY. ----------------------------------------------------------- 54

TABLE ‎4-6: INCREASE IN G1 ULTIMATE LOAD CARRYING CAPACITY WITH RESPECT TO UC AND MC. ---- 55

TABLE ‎4-7: INCREASE IN G1 MAXIMUM LONGITUDINAL AXIAL STRAIN WITH RESPECT TO UC AND MC. - 58

TABLE ‎4-8: G2 ULTIMATE LOAD CARRYING CAPACITY. ----------------------------------------------------------- 61

TABLE ‎4-9: INCREASE IN G2 ULTIMATE LOAD CARRYING CAPACITY WITH RESPECT TO UC AND MC. ---- 63

TABLE ‎4-10: DECREASE IN G2 MAXIMUM LONGITUDINAL AXIAL STRAIN WITH RESPECT TO UC AND MC.

------------------------------------------------------------------------------------------------------------------------ 66

TABLE ‎4-11: G3 ULTIMATE LOAD CARRYING CAPACITY. --------------------------------------------------------- 68

TABLE ‎4-12: INCREASE IN G3 ULTIMATE LOAD CARRYING CAPACITY WITH RESPECT TO UC AND MC. -- 69

TABLE ‎4-13: INCREASE IN G3 MAXIMUM LONGITUDINAL AXIAL STRAIN WITH RESPECT TO UC AND MC. 73

TABLE ‎4-14: SUMMARY OF THE RESULTS FOR ALL TESTED COLUMN SPECIMENS. ---------------------------- 77

X

LIST OF FIGURES

FIGURE ‎1-1: RESEARCH METHODOLOGY. ------------------------------------------------------------------------------- 5

FIGURE ‎2-1: THREE GROUPS LOAD DEFLECTION CURVES. ‎[6] ------------------------------------------------------ 9

FIGURE ‎2-2: DETAILING OF PLATES AND ANGLES. ‎[7] -------------------------------------------------------------- 10

FIGURE ‎2-3: CAMPIONE EXPERIMENTAL RESULTS COMPARED WITH OTHER STUDIES. ‎[9] -------------------- 11

FIGURE ‎2-4: LOAD VS. STRAIN RELATIONSHIP FOR CIRCULAR AND SQUARE COLUMNS. ‎[12] ---------------- 12

FIGURE ‎2-5: GEOMETRY OF UN-JACKETED, HPFRC JACKETED AND TRADITIONAL JACKETED SECTIONS

FROM LEFT TO RIGHT RESPECTIVELY. ‎[23] -------------------------------------------------------------------- 15

FIGURE ‎2-6: M-N ENVELOPES FOR THE THREE ANALYZED STRENGTHENING TECHNIQUES. ‎[23] ----------- 15

FIGURE ‎2-7: GEOMETRIC PROPERTIES AND REINFORCEMENT OF THE FOUR SIDES JACKETED COLUMNS. ‎[24]

------------------------------------------------------------------------------------------------------------------------ 16

FIGURE ‎2-8: GEOMETRIC PROPERTIES AND REINFORCEMENT OF THE THREE SIDES JACKETED

COLUMNS. ‎[24] ----------------------------------------------------------------------------------------------------- 17

FIGURE ‎2-9: LOAD–DISPLACEMENT RELATIONSHIPS FOR TESTED SPECIMENS. ‎[25] --------------------------- 18

FIGURE ‎2-10: CROSS SECTION OF SPECIMENS. ‎[27] ----------------------------------------------------------------- 19

FIGURE ‎2-11: LOAD-STRAIN CURVES OF COLUMN SPECIMENS.‎[27] ---------------------------------------------- 19

FIGURE ‎2-12: GEOMETRY OF CROSS SECTION AND BENT DOWN STEEL CONNECTOR. ‎[28] ------------------- 20

FIGURE ‎2-13: LOAD AGAINST DISPLACEMENT ENVELOPES FOR ALL SPECIMENS. ‎[28] ------------------------ 21

FIGURE ‎2-14: TYPES OF FIBERS. ---------------------------------------------------------------------------------------- 23

FIGURE ‎2-15: POLYPROPYLENE FIBERS.‎[4] --------------------------------------------------------------------------- 24

FIGURE ‎2-16: SLUMP FLOW, L-BOX AND V-FUNNEL TESTS. ------------------------------------------------------- 27

FIGURE ‎3-1: EXPERIMENTAL PROGRAM. ------------------------------------------------------------------------------ 30

FIGURE ‎3-2: GEOMETRY AND STEEL DETAILS OF UC UNJACKETED REFERENCE COLUMN. ------------------ 31

FIGURE ‎3-3: GEOMETRY AND STEEL OF MC1 MONOLITHIC CAST REFERENCE COLUMN. -------------------- 32

FIGURE ‎3-4: MAIN REBAR TENSION TEST. ---------------------------------------------------------------------------- 34

FIGURE ‎3-5: GEOMETRY AND STEEL DETAILS OF COLUMN CORE. ------------------------------------------------ 35

FIGURE ‎3-6: HANDLING FRESH NSC MIX FROM MIXING DRUM. ------------------------------------------------- 36

FIGURE ‎3-7: OILING AND CASTING TIMBER MOULDS. -------------------------------------------------------------- 36

FIGURE ‎3-8: THE AGGREGATES USED IN UHPSCC MIX. ----------------------------------------------------------- 38

FIGURE ‎3-9: FORTA-FERRO POLYPROPYLENE FIBERS.‎[4] ---------------------------------------------------------- 39

FIGURE ‎3-10: SIKAMENT 163M SUPERPLASTICIZER. ---------------------------------------------------------------- 40

FIGURE ‎3-11: SILICA FUME APPEARANCE ---------------------------------------------------------------------------- 40

FIGURE ‎3-12: GEOMETRY AND STEEL DETAILS OF G1-25, G2-25 AND G3-25. --------------------------------- 42

FIGURE ‎3-13: SHEAR CONNECTORS AND BONDING AGENT. ------------------------------------------------------- 43

FIGURE ‎3-14: COLUMN CORES LOCATED IN TIMBER MOULDS BEFORE CASTING.------------------------------ 44

FIGURE ‎3-15: THE COMPRESSION TESTING MACHINE -------------------------------------------------------------- 45

FIGURE ‎4-1: FAILURE PATTERN OF UC REFERENCE COLUMN. ---------------------------------------------------- 48

FIGURE ‎4-2: LOAD-STRAIN DIAGRAM OF UC REFERENCE COLUMNS. ------------------------------------------- 49

FIGURE ‎4-3: AVERAGE LOAD-STRAIN DIAGRAM OF UC REFERENCE COLUMN. -------------------------------- 49

FIGURE ‎4-4: ULTIMATE LOAD CARRYING CAPACITY OF UC AND MC REFERENCE COLUMNS. -------------- 50

FIGURE ‎4-5: LOAD-STRAIN DIAGRAM OF MC1 REFERENCE COLUMN. ------------------------------------------- 51

FIGURE ‎4-6: AVERAGE LOAD-STRAIN DIAGRAM OF MC1 REFERENCE COLUMN. ------------------------------ 51


FIGURE ‎4-8: AVERAGE LOAD-STRAIN DIAGRAM OF MC2 REFERENCE COLUMN. ------------------------------ 52


FIGURE ‎4-10: AVERAGE LOAD-STRAIN DIAGRAM OF MC3 REFERENCE COLUMN. ---------------------------- 52

FIGURE ‎4-11: LOAD-STRAIN DIAGRAMS OF UC, MC1, MC2 AND MC3 REFERENCE COLUMNS. ------------ 53

FIGURE ‎4-12: G1 ULTIMATE LOAD CARRYING CAPACITY.--------------------------------------------------------- 54

FIGURE ‎4-13: G1 ULTIMATE LOAD CARRYING CAPACITY WITH RESPECT TO UC AND MC. ------------------ 55

XI

FIGURE ‎4-14: LOAD-STRAIN DIAGRAM OF G1-25 JACKETED COLUMN SPECIMENS. --------------------------- 56

FIGURE ‎4-15: AVERAGE LOAD-STRAIN DIAGRAM OF G1-25 JACKETED COLUMN SPECIMENS. -------------- 56





FIGURE ‎4-20: AVERAGE LOAD-STRAIN DIAGRAM OF G1-25, G1-30 AND G1-35 ------------------------------- 58

FIGURE ‎4-21: AVERAGE LOAD-STRAIN DIAGRAMS OF G1-25, G1-30, G1-35 WITH RESPECT TO UC AND

MC.------------------------------------------------------------------------------------------------------------------- 59

FIGURE ‎4-22: FAILURE PATTERN OF UC REFERENCE COLUMN. --------------------------------------------------- 60

FIGURE ‎4-23: FAILURE PATTERN OF MC REFERENCE COLUMNS. ------------------------------------------------- 60

FIGURE ‎4-24: FAILURE PATTERN OF G1 JACKETED COLUMN SPECIMENS. -------------------------------------- 61









FIGURE ‎4-33: AVERAGE LOAD-STRAIN DIAGRAM OF G2-25, G2-30 AND G2-35. ------------------------------ 66


MC.------------------------------------------------------------------------------------------------------------------- 67





FIGURE ‎4-39: AVERAGE LOAD-STRAIN DIAGRAM OF G3-25 JACKETED COLUMN SPECIMENS --------------- 71

FIGURE ‎4-40: LOAD-STRAIN DIAGRAM OF G3-30 JACKETED COLUMN SPECIMENS ---------------------------- 71


FIGURE ‎4-42: LOAD-STRAIN DIAGRAM OF G3-35 JACKETED COLUMN SPECIMENS ---------------------------- 72


FIGURE ‎4-44: AVERAGE LOAD-STRAIN DIAGRAM OF G3-25, G3-30 AND G3-35. ------------------------------ 72


MC.------------------------------------------------------------------------------------------------------------------- 73


FIGURE ‎4-47: G1, G2 AND G3 ULTIMATE LOAD CARRYING CAPACITY WITH RESPECT TO UC AND MC. -- 75

FIGURE ‎4-48: G1-25, G2-25 AND G3-25 LONGITUDINAL AXIAL STRAIN WITH RESPECT TO UC AND MC1.76



XII

NOTATIONS

ABBREVIATIONS

UHPC Ultra High Performance Concrete

FFP Forta-Ferro Polypropylene

SCC Self-Compacting Concrete

UHPSCC Ultra-High Performance Self-Compacting Concrete

CFRP Carbon Fiber Reinforced Polymer

RC Reinforced Concrete

ACI American Concrete Institute

FRP Fiber Reinforced Polymer

NSC Normal Strength Concrete

ASTM American Society for Testing and Materials

HPFRC High Performance Fiber Reinforced Concrete

HPC High Performance Concrete

W/C Water Cement Ratio

IUG Islamic University-Gaza

KN Kilo Newton

MPa Mega Pascal

NOMENCLATURE

h/b Height to Breadth Ratio

UC Unjacketed Column Specimen(Reference Column)

MC Monolithically Cast Column Specimen (Reference Columns of Three

Cross Sections )

G1 Group of 9 Column Cores Strengthened with Fibrous UHPSCC

Jacket

G2 Group of 9 Column Cores Strengthened with Non-Fibrous UHPSCC

Steel Reinforced Jacket

G3 Group of 9 Column Cores Strengthened with Fibrous UHPSCC Steel

Reinforced Jacket

S Sample of Column specimen

fy Steel Yield Strength

fc’ Compressive Strength of Concrete Standard Cylinder

CHAPTER 1INTRODUCTION

CHAPTER 1 INTRODUCTION

2

1.1. Introduction

Repairing and strengthening of reinforced concrete (RC) elements is required for

several reasons, namely; damages, extension of lifetime and serviceability of structure,

lack of structure maintenance and degradation. Other reasons can be considered like the

retrofitting of the structure to meet the current design codes and regulations. Structural

members may need to be upgraded to current seismic requirements, as existing

structural components may be deficient in terms of seismic strength which can be

attributed to an inadequate transverse steel reinforcement. Strengthening such elements

is a method to increase the flexural, axial and shear strengths.‎[1, 6 and 7]

Strengthening methods depend on the type of the structure and loading, as for structures

subjected mainly to static load, increasing flexural and axial compressive strength is

more considerable, and for structures subjected mainly to dynamic load, increasing

flexural and shear strength is more considerable. Improving column ductility and

rearrangement of column stiffness can also be achieved by strengthening. Damages to

RC columns may include slight cracks without damages to reinforcement, superficial

damage in concrete without damage to reinforcement, concrete crushing, reinforcement

buckling or ties rupture. Based on the degree of damage, techniques such as injections,

removal and replacement or jacketing can be applied. ‎[7, 9, 22 and 23]

Five commonly jacketing techniques are used for strengthening the RC columns in

construction:

1) Concrete jacketing;

2) Steel jacketing;

3) Jacketing by Composite Materials (Carbon Fiber Reinforced Polymer CFRP);

4) Precast Concrete Jacketing;

5) External Pre-stressing Jacketing using Steel Strands;

Ultra High Performance Concrete (UHPC) is being considered for use in a wide variety

of mega structure applications. The high compressive and tensile strength allow for the

redesign and optimization of structural elements. Concurrently, the enhanced durability

properties facilitate a lengthening of design life and allow for potential use as thin

overlays, claddings, repairing and jacketing of columns.‎[2, 3, 23 and 26]

Despite UHPC has very high compressive strength, it shows very brittle failure behavior

compared to the Normal Strength Concrete (NSC). The UHPC ductility and fracture

brittleness can be improved by adding fibers, so the addition of fibers in producing

UHPC will add innovative features to the structures and open new areas of UHPC

applications.‎[3, 26, 35 and 37]


3

During the last two decades, increased productivity and improved working environment

have had high priority in the development of concrete construction, so there is another

new concrete produced which is Self-Compacting Concrete (SCC). The main goal

behind the rapid growing of SCC is the easiness in placement and casting in heavily

reinforced and inaccessible areas. In addition, SCC increases productivity levels leading

to shortened concrete construction time and reducing the effort of concrete compacting

which leads to reduction in honeycombing and segregation problems.‎[3, 35 and 37]

The addition of fibers reduced plastic and hardened concrete shrinkage, improves

impact strength, increases both fatigue resistance and toughness of the UHPSCC.

Moreover it greatly improves the tensile strength of the UHPSCC as well as the

ductility.‎[4, 34 and 36]

This research will study the strengthening of square RC columns by applying three

concrete jacketing styles using Forta Ferro Polypropylene Fibrous Ultra High

Performance Self-Compacting Concrete (Fibrous UHPSCC) as a jacketing material.

1.2. Problem Statement

Gaza strip has suffered many destructive wars leaving thousands of damaged buildings

either partially or totally, for instance; the 2008/2009 war on Gaza has left about 4,100

residential units completely devastated and 17,000 units suffered partial destruction. ‎[5]

RC columns are considered to be very fundamental structural member in buildings

subjected to damages, that need to be strengthened or repaired using the most adequate

and effective technique.

In the meantime, more and more structural engineers are forced to consider maintenance

or strengthening of existing RC columns as a must, either for old or new RC columns,

because of the following reasons: ‎[6, 7 and 8]

1) New structures that may include unsafe columns due to bad workmanship or due to

errors in modeling and design. Such cases, although not very frequent, have to be

dealt with taking into consideration the need to preserve the shape and size of the

column without altering the intended functional use of the structure and at the same

time without compromise to the structural integrity and safety.

2) The need to place additional loads on columns due to the change in building

regulations, this includes either the permission to add more floors, or the change of

the allowed occupational use of the structure. Such changes are known to happen

especially in largely populated area.

3) Aging of old structures due to deterioration of concrete, corrosion of reinforcing

steel bars or both, which leads to the loss of strength of columns and the inability to


4

carry design loads. These structures may be of historical or monumental values and

could be considered as part of local heritage, or they could be ordinary structures

that simply cost less to repair and maintain than to demolish and reconstruct.

4) Occasionally, some structures or part of them are subjected to accidents such as

fire, explosions or shelling and thus reducing column carrying capacity.

In some design manuals, retrofitting of circular columns is being recommended for

strengthening of columns, while square and rectangular columns are being considered

on a case by case basis.

Since most of the columns in residential and office buildings in Gaza are of square or

rectangular shapes, it could be concluded that there is a badly need for such a

strengthening technique of RC non-circular columns.‎[6, 7 and 12]

That boosted searching for a reliable, effective and easy applicable RC columns

strengthening technique by applying the Fibrous UHPSCC as a jacketing material.

1.3. Research Objectives

The main goal of this research is to strengthen the full height of square RC columns by

applying Fibrous UHPSCC jacket on four column sides. To achieve this goal, the

following objectives are considered:

1) Investigate the ultimate load carrying capacity and the maximum longitudinal axial

strain of square RC columns strengthened using Fibrous UHPSCC jacket.

2) Study the effectiveness of the applied three jacketing styles in terms of ultimate

load carrying capacity, ductility and failure patterns, and compare the obtained

results with that of the reference columns.

3) Study the effect of jacket thickness on both the ultimate load carrying capacity and

the longitudinal axial strain and compare the obtained results with that of the

reference columns.

1.4. Methodology

The following methodology was followed to achieve the research objectives:

1) Previous studies related to the current research were comprehensively reviewed to

identify the main aspects of RC columns strengthening techniques with deep

investigation paid to the concrete jacketing technique. The history and constituent

materials were studied for the Fibrous UHPSCC, see Figure ‎1-1.

2) Experimental program was set up to investigate the properties and mixing

proportions of Normal Strength Concrete (NSC) and Fibrous UHPSCC, properties


5

of steel, the interface bonding technique between column core and jacket, casting

and curing procedures for jacketed and reference column specimens.

3) Uniaxial compression loading tests were carried out to study the ultimate load

carrying capacity and the longitudinal axial strain of the jacketed and reference

column specimens at Materials and Soil Laboratory in the Islamic University-Gaza

(IUG).

Figure ‎1-1: Research Methodology.

4) Testing results of the jacketed column specimens were collected, refined, analysed

drawn and compared to that of the reference columns.

5) Conclusions and recommendations were issued based on the experimental program

results and data analysis.

1.5. Thesis Layout

This research contains five chapters listed as in the following:

1) Introduction (Chapter 1)

This chapter gives some background on the importance of strengthening RC columns

using different strengthening techniques, and a description for the research importance,

objectives, methodology and report organization.

2) Literature Review (Chapter 2)

This chapter reviews previous studies related to the subject of the current research to

identify the main aspects of RC columns strengthening techniques with deep

investigation paid to the concrete jacketing technique. The history and constituent

materials of Fibrous UHPSCC were also studied in this chapter.

PHASE 1

Literature Review

PHASE 2

Experimental Program

PHASE 3

Testing Column Specimens

PHASE 4

Collecting, Refining and Ananlyzing

Results

PHASE 5

Conclusions & Recommendatio

ns


6

3) Experimental Program (Chapter 3)

This chapter investigates the properties and mixing proportions of NSC and Fibrous

UHPSCC. Also, studies the properties of steel, the interface bonding technique between

column core and jacket, casting and curing procedures, and the application of uniaxial

compression load on the jacketed and reference columns.

4) Results & Discussion (Chapter 4)

This chapter analyzes, discusses and compares the obtained testing results of the

jacketed and reference columns in terms of ultimate load carrying capacity, longitudinal

axial strain and failure patterns.

5) Conclusions and Recommendations (Chapter 5)

This chapter includes the concluded remarks, main recommendations drawn from the

research work.

CHAPTER 2LITERATURE REVIEW

CHAPTER 2 LITERATURE REVIEW

8

2.1. Introduction

This chapter reviews the literature of the available previous studies related to several

strengthening techniques of RC columns, with particular attention devoted to

strengthening square RC columns by concrete jacketing. The properties, history and

application of the Fibrous UHPSCC as a jacketing material were also studied in this

chapter. Restoration, repairing and strengthening are defined below to accurately

distinguish between them:

1) Restoration is improving the damaged buildings so that they can be used again.

2) Repairing is retrieving back the structural performance of damaged buildings to

their original status.

3) Strengthening is improving the structural performance of damaged buildings

beyond their original levels.

Strengthening of existing structures has become a major part of the construction

activity in many countries. This can be attributed to the problems of concrete

structures aging, steel corrosion, variations in temperature, freezing-thawing cycles and

exposure to elevated heat.‎[1, 7 and 8]

2.2. Strengthening Techniques of RC Columns

The susceptibility of the existing buildings to structural damages largely depends on the

quality of design, detailing and construction. The engineer in many cases can extend

the life span of a building by utilizing a simple repair or strengthening technique. The

choice of repairing or strengthening technique becomes therefore the decisive factor as

the high cost would prevent many building owners from executing essential repair

works.‎[7, 8, 24 and 28]

Many previous studies have investigated the efficiency of several jacketing techniques

of RC columns as will be discussed in the following sections.

Jacketing RC Columns using Steel Profile 2.2.1.

Steel profile or hoops are used in different shapes to confine and enhance both ductility

and ultimate load carrying capacity of RC columns. Several previous studies focused on

the advantages and disadvantages of this technique.

Bsisu ‎[6] proposed that strengthening square RC columns to resist increased loads by

retrofitting with steel jackets is common engineering practice for strengthening and

repair of columns, as it is inexpensive, does not require highly trained labor,

unobtrusive, does not reduce space, easy to inspect and can be applied whilst the

structure is still in use. The study included three square columns groups; Group 1

consisted of 5 column specimens, intended to test the strength of RC columns retrofitted

with full steel jackets under concentric axial loading. Group 2 consisted of 5 column


9

specimens, intended to test the strength of confined concrete columns with steel jackets

not extending to the full height of the column under concentric axial loading. Group 3

consisted of 5 specimens of RC columns without retrofitting, tested under concentric

axial loading. Figure ‎2-1 shows the experimental plotted results of the columns groups,

and following points were concluded:

1) Retrofitting square RC columns with full steel jackets can enhance the compressive

strength of these columns more than double the strength of the original column.

2) The confined strength of concrete is approximately 1.5 times the unconfined

strength.

3) Confinement of RC columns with full steel jacket can enhance the ductility and the

ultimate strength of the column subjected to eccentric axial loading.

Figure ‎2-1: Three Groups Load Deflection Curves. ‎[6]

Jacketing RC Columns by External Steel Battens Welded to Steel Angles 2.2.2.

Steel plates and angles are used in strengthening RC columns and beams to increase the

load carrying capacity. This technique is properly and effectively applied in the cases

where the member dimensions are not permitted to be increased based on usage or

architectural limitations.

Frangou et al. ‎[7] proposed a cost effective and efficient technique for strengthening

square RC columns. The proposed technique involves post tensioning metal strips

around RC columns, by using a strapping machine, see Figure ‎2-2. The preliminary

results of the carried out experimental work indicate that such strengthening can

increase member strength and ductility to higher levels than those possible by


10

conventional reinforcement, at a fraction of the time and cost required by alternative

techniques. The study concluded the followings findings:

1) The strapping technique has been demonstrated to effectively strengthen specimens

tested axially and in bending. The low cost of the materials used, and the ease and

speed of application make this technique very competitive for the repair and

strengthening of RC columns.

2) A very important factor contributing to the success of the strapping technique is the

fact that a tensioning force is applied. The lack of such a force could lead to a

devastating reduction in the effectiveness of confinement.

Figure ‎2-2: Detailing of Plates and Angles. ‎[7]

Campione ‎[9] studied the response on square RC columns externally strengthened with

steel angles and battens subjected to axial force and bending moment. The original

contribution of the study was the investigation of the effect of steel angles and strips

externally welded to the RC columns both in term of moment axial forces increments

and available ductility. Finally parametric analyses in term of available ductility and

moment curvature diagrams were carried out to highlight the effectiveness of this

reinforcing technique. The following remarks were drawn:

1) If the pitch of strips is low and respects limits given by most of the existing codes

(lower than 0.5 column width) buckling effects do not penalize the load carrying

capacity of steel angels and high confinement effects on concrete core are reached.

2) The increment in the load carrying capacity of the strengthened members is

significant both in term of axial force and bending moment due to the coupled

effects of confinement on concrete core and due to the composite action.

3) Significant increases in ductility are achieved by using steel angles and strips also

with very high levels of axial forces, reaching up to 10.


11

Figure ‎2-3: Campione Experimental Results Compared with other Studies. ‎[9]

Finally, comparison was made between obtained experimental results and results from

other studies as shown in Figure ‎2-3.

Jacketing RC Columns by FRP 2.2.3.

Applications of Fiber Reinforced Polymer (FRP) for retrofitting and strengthening

existing concrete structures have been rapidly growing all over the world, this

strengthening technique provides an efficient, non-corroding alternative to externally

bonded steel plates. The purpose of retrofitting by FRP composite strengthening

systems is to strengthen or improve the flexural capacity, shear capacity, axial capacity,

and ductility, or any combination of them.‎[10, 11, 14 and 16]

The high durability of FRP is valuable in environments that may cause steel

corrosion. FRP is gaining popularity in view of its many advantages such as low unit

weight, ease of handling and application, and low installation and maintenance costs.

The principal disadvantage of FRP composite strengthening systems is its high cost,

lack of availability, requirement of high experienced workmanship in application and

low resistance against elevated temperatures. FRP can be used to strengthen columns in

compression, shear, and flexure by placing on the external faces of columns.‎[11, 14 and

17]

Esfahani el al. ‎[12] studied the axial compressive strength of columns strengthened by

FRP wrap. The experimental part of the study included testing 6 RC columns in two

series. The first series comprised three similar circular RC columns strengthened with

FRP wrap. The second series consisted of three similar square columns, two with sharp

corners, and the other with rounded corners. Axial load and strain were recorded during

tests using a displacement control test set up.


12

It was shown that the FRP wrap increased the strength and ductility of circular columns

significantly. Based on test results, the FRP wrap did not increase the strength of square

columns with sharp corners. However, the square column with rounded corners

exhibited a higher strength and ductility compared to those with sharp corners,

Figure ‎2-4 explains the plotted test results.

Figure ‎2-4: Load vs. Strain Relationship for Circular and Square Columns. ‎[12]

The following conclusions were drawn based on the study results:

1) The test results of wrapped circular columns have shown that the FRP wrap can

increase the axial strength of circular columns significantly. The ductility of

circular columns has been improved by applying the FRP wrap.

2) The application of FRP wrap may not increase the axial strength of square columns.

However, if the corners of the square columns are rounded appropriately, the axial

strength and ductility of columns increase considerably.

Toutanji ‎[17] investigated the performance of concrete columns confined with FRP

composite sheets. Concrete columns were wrapped with three different types of FRP

composites. Axial load and axial lateral strains were obtained to evaluate stress-strain

behavior, ultimate strength, stiffness, and ductility. The results showed that both the

strength and ductility of tested specimens were significantly enhanced over the

unwrapped specimens. In addition, an analytical model was developed to predict the

entire stress-strain relationship of the wrapped specimens.

Results from a series of experimental tests on concrete confined with FRP sheets

compared favorably with the results obtained by the proposed model. Confinement

effectiveness of FRP jackets in concrete columns was studied by a number of

researchers like Saafi et al. ‎[18] and Mirmiran ‎[19]. The improvement in mechanical

properties depends on several parameters, including concrete strength, types of fibers


13

and resin, fiber volume fraction and fiber orientation in the jacket, jacket thickness,

shape of cross section, column length diameter ratio, and the interface bonding between

core and jacket.

Spoelstra and Monti ‎[20] developed a uniaxial model for concrete confined with FRP.

The model explicitly accounted for the continuous interaction with the FRP wrap due to

the lateral strain of concrete through an incremental iterative approach. The relation

between the axial and lateral strains was implicitly derived through equilibrium between

the dilating confined concrete and the wrap. The model was compared with a set of

experimental tests, and showed very good agreement in both the axial stress- strain and

the stress-lateral strain response.

Seible et al. ‎[21] conducted a large scale test on one as built and four composite

wrapped rectangular flexural bridge spandrel columns to assess the effectiveness of

different retrofit schemes using FRP composite jackets. The tests showed that FRP

composite jacketing systems clearly can be installed without affecting the overall

geometry or appearance of the structure. They emphasized the importance of designing

retrofit strategies to control the mode of failure. Retrofitting one weakness without

considering other potential modes of failure could lead to ineffective and poor designs.

Strengthening RC Columns by Concrete Jacketing 2.2.4.

There are many factors affecting the behavior of strengthened RC columns by concrete

jacketing, these factors can be summarized as follows:

1) Concrete compressive strength of the original column.

2) Concrete jacket thickness.

3) Stress level of the original column.

4) Amount and distribution of the transverse reinforcement of jacket.

5) Contact surface between the original column and the jacket.

6) Use of shear keys and shear connectors and their configuration.

7) Jacket height and loading area.

8) Rectangularity ratio of the original column.

9) End conditions of the original column.

10) Eccentricity of the applied loads.

11) Casting direction of concrete.

12) Position of the original column.

13) Concrete compressive strength of the RC jacket.

14) Vertical reinforcement of the RC jacket.


14

Experimental investigations of strengthened or repaired columns are generally

conducted on unloaded original columns, in spite of the fact that it is very difficult to

have an unloaded strengthened column in the field. Studying the behavior of

strengthened column with preloading the original column is very important but also is

very difficult experimentally.‎[22 and 25]

Allam ‎[22] carried out an experimental study to investigate the behavior of the original

columns and the effect of the jacket height while the original columns were under

loading. Six parameters affecting the behavior of strengthened RC columns were

studied; jacket thickness, stress level in the original column, concrete strength of the

original column, stirrups of jacket, shear connectors, and jacket height respectively. The

tested specimens were divided into six groups; each group was concerned with one of

the mentioned six parameters. The following points were concluded:

1) As the preloading stress in the original column increases the ultimate load of the

jacketed column decreases by 19%, 31%, and 42% for the cases of preloading by

the working load, 0.5 of the failure load, and 0.8 of the failure load respectively.

2) Vertical strains in the jacket decreases as the stress level increases in the original

column which means that jacket efficiency decreases as the stress level increases.

3) The lateral tensile strains at the top of the jacket increases as the stress level in the

original column increases after the first crack load.

4) In the case of the preloaded columns, the vertical strain at the top of the jacket is

less than that for the case of total release of load. In the case of the preloaded

columns, the vertical strain in the original columns is more than that in the case of

total release of load at the ultimate load. The Calculation of the strength of the

jacket as a RC column overestimates the strength. The overestimation increases in

case of preloaded columns over the cases of total release of load.

5) In the case of loading the original column and the jacket for the preloaded

columns, the ultimate load increased by 1.81 times the ultimate load for loading the

original column only.

6) In the case of total release of load, the ultimate load increased by 2.05 times the

ultimate load for loading the original column only.

Meda et al. ‎[23] Studied the possibility of strengthening existing RC columns with a

technique based on the application of a high performance fiber reinforced concrete

(HPFRC) jacket having 170MPa compressive strength. The geometry of unjacketed,

HPFRC jacketed, and traditional jacketed RC columns are ordered in Figure ‎2-5 from

left to right respectively.


15

Figure ‎2-5: Geometry of Un-jacketed, HPFRC Jacketed and Traditional Jacketed Sections from

Left to Right Respectively. ‎[23]

Both axial load (N) and bending moment (M) were analyzed by analytical drawing

interaction envelopes as seen in Figure ‎2-6. The obtained results were compared with

the response of columns strengthened with the traditional jacket, and the following were

concluded:

1) The use of HPFRC jacket for strengthening existing RC columns has shown that a

30 mm thick jacket allows a significant increase of the bearing capacity both under

flexure and axial force.

2) The maximum axial force of strengthened columns equal to 7800 KN which is four

times higher than the un-jacketed one.

3) The increase of the pure bending moment is more than 100%, with a maximum

value of about 140 KNm.

4) The HPFRC jacket led also to an increase of the maximum tensile force that equals

to about 1000 KN and is more than double with respect to the un-jacketed section.

5) The proposed technique was compared with the traditional RC jacket that requires

higher thickness of the jacket. The HPFRC jacketing resulted in great efficiency

particularly for the axial force strengthening.

6) This solution requires jacket with a very small thickness. Due to the good surface

quality that can be obtained by the HPFRC material, the jacket can substitute the

plaster layer with no significant change in the column size.

Figure ‎2-6: M-N Envelopes for the Three Analyzed Strengthening Techniques. ‎[23]


16

CAN ‎[24] has found in his research that the reinforced concrete columns were repaired

or strengthened by introducing a new reinforced concrete layer surrounding the existing

column as jacketing. Although four sided jacket is the most desirable type sometimes,

partial jacketing on two or three sides is inevitable due to space limitations, edge and

corner columns of buildings surrounded by close neighbors, Figure ‎2-7 and Figure ‎2-8

shows the geometric detailing of four and three sides jacketed columns respectively.

The four and three sided jacketed columns were experimentally investigated under

uniaxial loading, and the following results were reported:

Columns Jacketed on Four Faces

1) The jacketing for strengthening resulted in a column capacity of 92% of the

reference (monolithic) specimens.

2) There is no reduction in stiffness and ductility, only the axial load capacity is

reduced by 8%.

3) The jacketing for rehabilitation (repairing) has resulted in a column capacity of

88% of the reference (monolithic) specimens.

Figure ‎2-7: Geometric Properties and Reinforcement of the Four Sides Jacketed Columns. ‎[24]

Columns Jacketed on Three Faces

1) The jacketing for strengthening and rehabilitation (repairing) resulted in a column

capacity of 90% and 82% respectively of the reference (monolithic) specimens.


17

2) Column stiffness has increased by 40% in repaired specimens and 51% in reha-

bilitation (monolithic) specimens.

3) The strengthened column has dissipated 14% less energy and the repaired column

23% less energy as compared to the monolithic column.

Jacketing on all four faces is more efficient from strength and ductility points of view as

compared to jacketing on three faces only.

Figure ‎2-8: Geometric Properties and Reinforcement of the Three Sides Jacketed Columns. ‎[24]

Mourad et al. ‎[25] has investigated a series of 10 small scale square RC columns,

preloaded under axial compression up to various fractions (0%, 60%, 80%, and 100%)

of its ultimate load and repaired using high strength ferrocement jackets containing two

layers of steel reinforcement in high strength mortar then retested to failure. The overall

response of the specimens was investigated in terms of load carrying capacity, axial and

lateral displacement. Figure ‎2-9 superimpose the axial and lateral displacement with

load carrying capacity for control columns (SC-2), jacketed columns (SJ-0-2),

strengthened preloaded columns (SJ-60-1 and SJ-80-1) and strengthened failed column

(SJ-100-1).The study concluded the following points:

1) The test results indicated that jacketing reinforced concrete square columns with

high strength ferrocement provided about 33% and 26% increases in axial load

capacity and axial stiffness respectively, compared to the control columns.


18

2) The test results also indicated that repairing similar reinforced concrete columns

(after preloading them to failure) with the same ferrocement jacket almost restored

their original load capacity and stiffness. Furthermore, the repaired columns failed

in a ductile manner compared to the brittle failure exhibited by the control columns.

Figure ‎2-9: Load-Displacement Relationships for Tested Specimens. ‎[25]

Abdelrahman ‎[26] studied the jackets surrounding the full perimeter of the original

columns which are normally used for repair of the interior columns. The level of stress

in the column before repair is assumed to be relatively low to extent that the preloading

of the original column does not affect the overall behavior significantly. He also studied

the load application on only sectional area of the original column. It was found that the

load transfer from the original column to the jacket over a distance about 2 to 3 times

the breadth of the original column. The ultimate load of this strengthened column was

less than the increase in the cross sectional area.

Ersoy et al. ‎[27] carried out a research in repair and strengthening of columns by

jacketing. The columns were tested under uniaxial load, four basic columns having

identical dimensions and reinforcement were tested under monotonic axial loading.

After the test, the basic columns were jacketed and retested. The intervention was

called either a repair or strengthening jacket depending on whether or not the

basic specimens had been loaded to a damaged level.

Two of the specimens were jacketed after unloading the basic column, while the other

two were jacketed under loading (the load is still in practice), and both cases were

investigated. The original concrete columns have cross section of 13×13cm, 65cm in

length, 4Ø10 main steel reinforcement, and 25Ø4/m stirrups. While the jacketed

columns have cross section of 18×18cm, 65cm in length, 4Ø10 jacket reinforcement,

and 25Ø4/m jacket stirrups. Figure ‎2-10 shows the cross section of the specimens.


19

Figure ‎2-10: Cross Section of Specimens. ‎[27]

In addition to the four jacketed columns, a reference specimen (M) with dimensions and

reinforcement identical to those of the jacketed columns were tested, in this specimen

the basic column and the jacket were cast monolithically.

Axial load versus axial strain curves for the jacketed and monolithic specimens were

given in Figure ‎2-11. And the following points were concluded:

1) Strengthening jackets were quite effective. The specimen in which jacketing was

made under load (US) behaved almost as well as the one in which jacketing was

made after unloading (LS). Specimens with strengthening jackets reached from

90% to 95% of the capacity of the reference specimen.

2) The specimen with the repair jacket made after unloading (UR) behaved well and

reached 80% of the capacity of the reference specimen.

3) The specimen with the repair jacket made under load (LR) did not behave well and

failed when reached 80% of the reference specimen capacity.

Figure ‎2-11: Load-Strain Curves of Column Specimens.‎[27]


20

Vandoros and Dritsos ‎[28] have presented an investigation for the effectiveness of

using alternative techniques to place concrete jackets in order to strengthen RC

columns. See Figure ‎2-12 for detailed geometry. Three different jacket construction

procedures were used. In addition, for comparative purposes, the results from two

specimens strengthened using Carbon FRPs have been presented.

Figure ‎2-12: Geometry of Cross Section and Bent down Steel Connector. ‎[28]

On the other hand, as far as load capacity and initial stiffness are concerned, the

influence of the connection is less significant, providing that the anchorage of the

stirrup ends can be guaranteed by welding them together. They have reported that in

general, the strength and the stiffness of the strengthened specimens were lower than

that of the respective monolithic element.

However, when special bent down steel connectors were used to connect the original

column reinforcement bars to the jacket reinforcement bars, the energy dissipation rate

was higher than that of the monolithic specimen.

Therefore, as far as energy dissipation capacity is concerned, this technique in

combination with a shotcrete jacket seems to be the most effective. In addition, welding

the stirrup ends together stops the stirrups from opening and in turn, the longitudinal

bars of the jacket do not buckle resulting to better maximum load capacity.

Therefore, as far as maximum load capacity is concerned, the disadvantage of using a

poured concrete jacket instead of a shotcrete jacket can be offset by welding the stirrup

ends together. The failure mechanism and the observed crack patterns are influenced by

the strengthening method.

The separation of the jacket from the original column was obvious in the case where

there was no treatment or other connection means performed at the contact interface

between the column and the jacket, See Figure ‎2-13 for the plotted results. Insert table

to denote the symbols of figure


21

Figure ‎2-13: Load against Displacement Envelopes for All Specimens. ‎[28]

The study demonstrated that placing concrete jackets around columns considerably

increases the strength and the stiffness while placing Carbon FRPs considerably

increases the ductility.

Ramirez ‎[29] performed an experimental study to compare the characteristics and

effectiveness of ten RC column repair methods. The repair is performed in order to

counterbalance a significant or total loss of carrying capacity. The methods presented

are divided into two groups. The first deals with the strengthening of the entire

column height, while the second focuses on the problem of damage and loss of strength

on a localized section. Different kinds used of standard and polymeric concrete jackets,

steel profiles, bonded, welded or bolted plate jackets and encasements.

Considering the first six methods that extend along the entire column height, the most

interesting methods, in terms of efficiency and cost, appear to be the simple concrete

jacket, and the steel angle method. The simple concrete jacket is easy to construct, and

the transmission of load is direct. It is advisable to make a special bar hoop

reinforcement at the two extremes of the jacket, close to the surfaces of the slab, to

improve the performance. This is necessary when the size of the original upper column

is smaller than that of the strengthened one.

He also concluded that, the steel (I-beam method) is very interesting, because it is not

based exclusively on the shear resistance of the beams or slabs. It takes an important

amount of the column load from the upper column and transmits it to the lower

column in a direct mode. With respect to the last four repair methods, which extend

over a minimum length on either side of the defect, three of them, numbers 7, 8

and 9, are very effective.


22

Methods based on a polymeric resin concrete jacket or steel plate jacket with injection

of voids with resin mortar, numbers 7 and 9 respectively, present high efficiency at a

low or moderate cost. The ratio between the failure load following repair and the

theoretical prediction has been greater than 1, obtaining values of the same order of

magnitude as for undamaged virgin columns. The repairs are thin and short. The main

problems with them may be low resistance against fire. Procedure no. 8 consisting of

angle bars with pre stressed bolts, has a very good behavior and seems to be very

reliable, although it is expensive and troublesome to apply. It may be of interest for

emergency strengthening.

2.3. Fibrous Ultra High Performance Self-Compacting Concrete

The jacketing material applied in this research was the Forta-Ferro Polypropylene

Fibrous Ultra High Performance Self-Compacting Concrete (Fibrous UHPSCC), as

discussed later in this chapter. The following points are explaining the main related

concepts, components and keys of this material.

Ultra-High Performance Concrete (UHPC) 2.3.1.

The Ultra High Performance Concrete (UHPC) with a compressive strength more than

100 MPa and improved durability marks developing step in concrete industry. This high

performance material offers a variety of interesting applications. It allows the

construction of sustainable and economic buildings with an extraordinary slim design.

Its high strength and ductility makes it the ultimate building material e.g. for bridge

decks, storage halls, thin-wall shell structures and highly loaded columns. Beside its

improved strength properties, its outstanding resistance against all kinds of corrosion is

an additional milestone on the way towards no maintenance constructions.‎[30, 34 and

37]

UHPC has very special properties that are remarkably different to the properties of

normal and high performance concrete. UHPC is formulated by combining Portland

cement, silica fume, quartz powder, high range water reducer, water, and steel or

organic fibers. For complete utilization of UHPC’s superior properties, special

knowledge is required for production, construction and design.‎[30, 34 and 35]

Self-Compacting Concrete (SCC) 2.3.2.

A structural concrete which strongly deviates from NSC in the fresh state as it flows

without the application of additional compaction energy. SCC can be defined as a

concrete that is able to flow in the interior of the formwork, filling it in a natural manner

and passing through the reinforcing bars and other obstacles, flowing and consolidating

under the action of its own weight leaving no segregation or honeycombing

problems.‎[31 and 32]


23

The Developing History of UHPSCC 2.3.3.

The development of the high strength concrete HSC, SCC and UHPSCC are all

summarized in Table ‎2-1.‎

Table ‎2-1: UHPSCC Development.‎[32]

Year UHPC History Year SCC History

1950

Concrete with a compressive

strength of 34MPa was considered

as high strength concrete

1988 The first time SCC was

developed in Japan

1960 High strength concrete were

developed in labs of only 80MPa 1993

The prototype of self-compacting

concrete was first completed using

materials already on the market

1980

High performance concrete of

100MPa were developed in

Denmark for special applications in

the security industry and protective

defense constructions

1997 The SCC was used for the first

time in Europe in the civil works

1985 First research was conducted on

the applications of UHPC 2002

European specification and

guidelines were developed for SCC

More

recently

Compressive strengths

approaching 120MPa is used

More

recently

SCC is used commercially in

Japan, Europe, USA, … etc.

Some researches take place on matching the UHPC and SCC in one mix in order to develop the

UHPSCC, which is used recently in many special engineering structures.

Types of Fibers 2.3.4.

The addition of various types of fibers to mechanically improve or modify the

performance of concrete results in what is called fiber reinforced concrete or fibrous

concrete. The discrete reinforcing fibers are randomly dispersed within the concrete

matrix. The performance improvements attributed to fiber reinforced concrete have

been increased flexural, tensile, and dynamic strength, ductility, and toughness. The

types of fibers commonly used include: steel, glass, polymeric, carbon, asbestos, and

natural fibers. The polymeric type include: polypropylene, polyethylene, polyester,

acrylic, and aramid fibers, see Figure ‎2-14.‎[32 and 33]

Figure ‎2-14: Types of Fibers.

Type of Fibers

Steel Glass Polymeric

Polypropylene

Forta Ferro

Polyethylene Polyester Acrylic Aramid

Carbon Asbastos Natural Fibers


24

The use of fibers as reinforcement in concrete precedes the use of conventionally

reinforced concrete. Polypropylene fibers are used to provide what is termed secondary

reinforcement, or the encouragement of a desired material behavior such as decreased

plastic and shrinkage cracking and improved toughness. Several manufacturers have

been selling the fibers to improve the concrete's resistance to the formation of plastic

shrinkage cracking and as secondary reinforcement as a replacement for welded wire

fabric.‎[33, 34 and 35]

Polypropylene Fibers 2.3.4.1.

Polypropylene is a synthetic hydrocarbon polymer material, first introduced in 1957.

Currently polypropylene is the most widely used of the synthetic fibers for concrete

applications. Polypropylene is available in two forms, monofilament fibers and film

fibers. Monofilament fibers are produced by an extrusion process through the orifices in

a spinneret and then cut to the desired length.‎[33, 35 and 36]

The newer film process is similar except that the polypropylene is extruded through a

die that produces a tubular or flat film. This film is then slit into tapes and uniaxially

stretched. These tapes are then stretched over carefully designed roller pin systems

which generate longitudinal splits and these can be cut or twisted to form various types

of fibrillated fibers.

The fibrillated fibers have a net-like physical structure. The tensile strength of the fibers

is developed by the molecular orientation obtained during the extrusion process.

Polypropylene has a melting point of 165°C and can withstand temperatures of over

100°C for short periods of time before softening. It is chemically inert and any chemical

that can harm these fibers will probably be much more detrimental to the concrete

matrix. The fiber is susceptible to degradation by ultra violet radiation (sunlight) and

oxygen; however, in the concrete matrix this problem is eliminated. Monofilament

fibers were the first type of polypropylene fiber introduced as an additive in

polypropylene fiber reinforced concrete.‎[4, 34 and 35]

Figure ‎2-15: Polypropylene Fibers.‎[4]

Monofilament fibers are available in lengths of 1/2, 3/4, and 1-1/2 inches. The

monofilament fibers have also been produced with end buttons or in twisted form to


25

provide for greater mechanical anchorage and better performance. The exact chemical

composition and method of manufacture may vary slightly among producers. The main

types or geometry of fibers currently available from most producers are monofilament

and fibrillated.

The fibrillated fibers are usually manufactured in bundles or collated together and come

in lengths of 1/2, 3/4, 1-1/2, or 2 inches, see Figure ‎2-15. The term fibrillated (screen)

fiber derives from the manufacturing method used. The term collated means that the

fibrillated fibers are bundled together, usually with some type of water soluble glue

which will break up or dissolve in the fluid concrete mixture.‎[33, 36 and 37]

Forta Ferro Polypropylene Fibers 2.3.4.2.

Forta Ferro Polypropylene (FFP) fibers is composed of a high performance bundle

twisted fiber, appropriate for all concrete thin works and precast applications. It is

produced from 100% virgin copolymer polypropylene consisted of a twisted bundle

nonfibrillated monofilament and a fibrillated network fibers.

The twisted bundle delivery system ensures that the fiber mixes well into the concrete

and distributes evenly throughout the concrete matrix. The fiber absorbs maximum

energy without breakage and is designed to retain its cross sectional shape thus avoiding

brittle failure in high load situations, see Table ‎2-2.‎[4]

Table ‎2-2: Physical Properties of Forta Ferro Polypropylene Fibers.‎[4]

Materials: Virgin

Copolymer/Polypropylene

Form: Monofilament/Fibrillated Fiber System

Color: Gray

Acid/Alkali Resistance: Excellent

Specific Gravity: 0.91

Tensile Strength: 570-660 MPa

Length: 54mm, 38mm

Absorption: Nil

Compliance: ASTM C-1116

2.4. Properties of Fibrous UHPSCC

UHPSCC definition includes eight performance characteristics: freeze-thaw durability,

scaling resistance, abrasion resistance, chloride penetration, compressive strength,

modulus of elasticity, shrinkage, and creep. For today’s structures, materials are of five

distinctive properties: strength, durability, workability, sustainability and affordability.

The first three properties basically include all the eight performance requirements listed

above. Affordability is the cost; and high performance refers to the improvement in

some or all of these properties. Sometimes, we have to give up a little in one to gain a

little in the other. In general, all these properties improve with time. The four properties

were discussed one by one as follows.‎[30 and 31]

Strength 2.4.1.

The compressive and the tensile strength which may be achieved by UHPSCC depend

strongly on the concrete composition, in particular with regard to type and amount of

binders and the fine aggregates as well as the type and duration of curing. If ordinary


26

curing, The UHPSCC maximum compressive strength of 200 MPa can be reached at

room temperature of 20ºc. If the temperature is increased to 100ºc, the strength will

reach approximately to 250 MPa. A further increase of curing temperature to 250ºc is

accompanied with a strength gain of almost 400MPa. The addition of Forta Ferro

Polypropylene fibers (FFP) causes a small improvement of the compressive strength of

UHPSCC, but may significantly affect the strain capacity of the concrete.‎‎[28 and 29]

The investigations on the effect of FFP fibers on UHPSCC pointed an optimum fiber

content of about 1.5% by volume of mix. The UHPSCC compressive strength may

improve within range (1%-7%), while the flexural strength may improve within range

(16%-26%) according to the fiber content. It should be noticed that the tensile strength

may increase from (20%-30%) when FFP fibers range (0.5-2 %) by volume of the mix.

FFP fiber has incredibly enhanced the ductile behavior of the UHPSCC unlike the Non-

Fibrous UHPSCC.‎[30, 35 and 37]

Durability 2.4.2.

There is a large need of durable materials that last a long time and are easy to maintain.

UHPSCC does offer good potential in this respect. However, in an engineering world

that values performance records, a certain amount of time will be needed to assure

people that the long term performance of the material is what the laboratory tests have

shown us.

The UHPSCC has a very dense matrix with very small and discontinuous pores which

leads to extensively improved durability properties compared to normal strength

concrete (NSC) and high performance concrete (HPC).

However, steam based curing increases the concrete hydration, improves the concrete

microstructure, and reduces its permeability, thereby it increases significantly the

UHPSCC durability properties. For example, the abrasion resistance can be largely

increased whereas the ability of chloride ion to penetrate into the concrete was

decreased.[29, 34 and 36]

Workability 2.4.3.

To design the mix of SCC, three workability parameters (filling ability, passing ability

and segregation) need to be assessed as shown in Table ‎2-3. A full scale test should be

used to verify the self-compacting characteristics of the targeted design for a particular

application. While for site quality control, two test methods are generally sufficient to

monitor the production quality namely the Slump-flow and V-funnel. ‎[37 and 39]

Table ‎2-3: EFNARC Criteria of Self-Compacting Concrete. ‎[37]

Method Unit Minimum Range Maximum Range

Slump Flow (Abram Cone) mm 550 850

T500mm Slump Flow S 2 9

V-Funnel S 6 12

L- Box (h2/h1) - 0.7 1.0


27

The low water cement ratio W/C less than 0.35 and the high fineness of silica fume

formed a high viscous paste, which led to a high reduction in the porosity of the

UHPSCC mix and improved its impermeability. The low W/C also resulted in a

significant increase in durability and strength of the UHPSCC mix. Figure ‎2-16 shows

the experimental apparatus used for Slump flow, L-Box and V-Funnel tests.

Figure ‎2-16: Slump Flow, L-Box and V-Funnel Tests.

However, in order to ensure the three workability parameters and SCC behavior; a high

range water reducer should be added to the UHPSSC mix to enable casting very slender

concrete elements without segregations or honeycombing. ‎[33, 35 and 37]

Sustainability 2.4.4.

UHPSCC is a green technology which supports the concept of sustainable development.

In other words, using UHPSSC enables slender sections thereby, using less cement in

the concrete and using less concrete in the members. Reports of many scientists

worldwide warned from global warming considering it as the most destructive problem

which people encounter nowadays. Using UHPSCC can preliminary save embodied

energy and reduce carbon dioxide emissions compared to conventional approaches. In

addition, its sustainability is even more considerable than others types of concrete with

respect to life cycle specimens compared to conventional RC.‎[31, 35 and 37]

Affordability 2.4.5.

Cost is often a determining factor on whether a structure will be built or not. There are

probably other good construction materials that can be used for construction except that

their high cost may have prevented them from being used. A potentially good but

expensive material may become affordable when its application is more widespread due

to mass production, while its application can only get widespread if its cost is

sufficiently low. The Fibrous UHPSCC has proved its affordability and cost

effectiveness compared with other applied materials during last decades. ‎[30 and 36]

2.5. Summary of Literature Review

From previous literature study the following remarks were concluded:

The majority of buildings in Gaza strip especially the residential buildings are

constructed with non-circular RC columns. Many problems appear when there is

necessity to increase the number of floors or loads on the RC columns. The importance

of strengthening RC columns became a must to accommodate such this condition.


28

Many possible strengthening techniques are applicable and can be successfully used but

have some limitations such as, adopting FRP jackets which is effective but has

problems of fire resistance and ultra violet lights, jacketing RC columns by steel plates

welded to angles which is inapplicable easily and needs high skilled workmanship.

Strengthening RC columns using traditional concrete jackets is an effective and easy to

apply technique but excessively increases the column section geometry.

Appling the Fibrous UHPSCC as a jacketing material for the RC columns can overcome

many limitations existing in the other strengthening techniques; no huge enlargement in

cross sections and thus preserve the free available usable space, high strength to volume

ratio and no resin or primer interposition is needed, flowing under its own weight,

perfectly filling the formworks and confirming adequate placing and compaction with

no need of vibration.

Using Fibrous UHPSCC prevents the honeycombing and segregation problems even

when casting slim forms or high steel congested sections. The Fibrous UHPSCC is

durable, sustainable, easy to manipulate by unskilled workmanship and its constituents

are available in local Gaza markets.

In this research, Fibrous UHPSCC was adopted as a jacketing material to strengthen the

entire height and four sides of square RC columns using three jacketing styles.

CHAPTER 3EXPERIMENTAL WORK

CHAPTER 3 EXPERIMENTAL WORK

30

3.1. Introduction

The main objective of this chapter is to specify and define the geometry and steel

configuration of the test specimens, instrumentation, mixing proportions of the normal

strength concrete (NSC) and the Ultra High Performance Self-Compacting Concrete

(UHPSCC).

The properties of steel, Fibrous and Non-Fibrous UHPSCC were investigated in this

chapter as well as the mechanical interface bonding, casting and curing procedures of

the fabricated column specimens.

3.2. Experimental Program

The experimental work carried out in this research has been planned to investigate the

ultimate load carrying capacity and longitudinal axial strain of uniaxially loaded square

RC columns strengthened using three jacketing styles. The obtained results were

compared with that of the reference columns. Figure ‎3-1 presents the experimental plan

of column specimens’ fabrication.

Figure ‎3-1: Experimental Program.

Experimental Program

Unjacketed Reference

Column, 100×100mm

Monolithic Reference

Columns

Reference Column,

150×150mm

Reference Column,

160×160mm

Reference Column,

170×170mm

Column Cores, 100×100mm

Application of

UHPSCC Jackets

Fibrous UHPSCC Jacket

25mm Jacket Thickness

30 mm Jacket Thickness


Steel Reinforced

Non-Fibrous

UHPSCC Jacket


30 mm Jacket Thickness

35mm Jacket Thickness,

Steel Reinforced

Fibrous UHPSCC

Jacket

25mm Jacket

Thickness

30 mm Jacket

Thickness

35mm Jacket

Thickness

Prepare NSC Mix


31

3.3. Categorizing The Column Specimens

The current study included fabricating a total of 39 column specimens; 12 column

specimens were fabricated to act as reference columns, while 27 column cores were

fabricated to be strengthened later in this study by applying the three jacketing styles

using Fibrous and Non-Fibrous UHPSCC jacket.

All column specimens were designed in compliance with the ACI 318-11 code

requirements. The adopted steel reinforcement ratio of all RC column sections was not

less than 1%. Details of the fabricated column specimens are as follows:

1) A square RC column specimen (UC) was casted monolithically to act as an

unjacketed reference column (similar to the column core). This reference column

has a cross sectional dimensions of 100×100mm and a height of 300mm, with

4Ø10 mm longitudinal steel reinforcement and 4Ø4 mm steel stirrups. Figure ‎3-2

shows the geometry and steel configuration of UC reference column.

Figure ‎3-2: Geometry and Steel Details of UC Unjacketed Reference Column.

2) Three square RC column specimens (MC1, MC2 and MC3) were casted

monolithically to act as reference columns. These reference columns have cross

sectional dimensions of 150×150, 160×160 and 170×170mm respectively, and a

height of 300mm, with 4Ø10 mm longitudinal steel reinforcement and 4Ø4 mm

steel stirrups. Figure ‎3-3 shows the geometry and steel configuration of MC1

reference column.


32

Figure ‎3-3: Geometry and Steel of MC1 Monolithic Cast Reference Column.

3) Three jacketing styles were applied on three groups of column cores (G1, G2 and

G3); Group1 (G1) consisted of nine column cores jacketed by Fibrous UHPSCC

without steel reinforcement, Group2 (G2) consisted of nine column cores jacketed

by Non-Fibrous UHPSCC with steel reinforcement, and Group3 (G3) consisted of

nine column cores jacketed by Fibrous UHPSCC with steel reinforcement.

4) Three jacket thicknesses of 25, 30 and 35mm were applied for the three groups of

column cores (G1, G2 and G3).

5) The overall cross sectional dimensions of G1, G2 and G3 jacketed column

specimens became 150×150, 160×160 and 170×170mm having jacket thicknesses

of 25, 30 and 35mm respectively and fixed height of 300mm.

6) The test result of every column specimen was the average of three samples of

column specimens (S1, S2 and S3). This is to increase the confidence in the

measured results.

7) Mechanical bonding technique was considered in this study by applying post

installed shear connectors to bond the new and old concrete.

8) L-Shape shear connectors were applied on the four faces of the column cores and

inserted in drilled holes with epoxy bonding agent as will be discussed later in this

chapter. Table ‎3-1 briefs the 39 column specimens studied in the experimental

program.


33

Table ‎3-1: Details of Column Specimens.

# Description Not.

Column Core

(mm), 300mm

Height, NSC

Mix

Overall Cross

Section (mm),

300mm Height,

UHPSCC Mix

Jacket

Thicknes

s (mm)

Number of

Samples

1 UC Unjacketed

Reference Column UC 100×100 Cross sectional dimensions of

UC and MC reference

columns are fixed, the jacket

is inexistent Three

samples (S1,

S2 and S3)

were

fabricated for

each column

specimen

2 MC Monolithically Cast

Reference Columns

MC1 150×150

3 MC2 160×160

4 MC3 170×170

5 Fibrous UHPSCC Jacket,

[G1]

G1-25 G1, G2 and G3

column cores

have similar

cross sectional

dimensions of

100×100 mm

and a height of

300mm

150×150 25

6 G1-30 160×160 30

7 G1-35 170×170 35

8 Steel Reinforced Non-

Fibrous UHPSCC Jacket,

[G2]

G2-25 150×150 25

9 G2-30 160×160 30

10 G2-35 170×170 35

11 Steel Reinforced Fibrous

UHPSCC Jacket, [G3]

G3-25 150×150 25

12 G3-30 160×160 30

13 G3-35 170×170 35

3.4. Types of Concrete Mixes

In this research, three concrete mixes were designed with different mixing proportions

depending on the targeted concrete compressive strength as below:

1) Preparation of the normal strength concrete mix (NSC) to cast the UC reference

column, MC reference columns and the column cores of the three groups G1, G2

and G3.

2) Preparation of Fibrous Ultra High Performance self-Compacting Concrete (Fibrous

UHPSCC) to cast the jacket of the G1 and G3 column specimens.

3) Preparation of Non-Fibrous UHPSCC to cast the jacket of the G2 column

specimens.

3.5. Preparation of UC, MC Reference columns and Column Cores

Normal strength concrete (NSC) mix was prepared to obtain targeted standard cylinder

compressive strength of about 20MPa. The low targeted strength represented the real

status of the majority of damaged RC columns in real life.

Properties of NSC Ingredients 3.5.1.

Concrete is a composite material made up of several different constituents such as

aggregate, sand, water, cement and admixture. The NSC ingredients are available in

local Gaza markets and selected of traditional conditions to represent the realistic state

of RC columns as follows:

1) Two types of aggregate were used, coarse and fine. The coarse aggregate size

ranges from 4.75mm to 17.5mm as available in Local markets. The Fine

Aggregate (sand) ranges from 0.3 to 0.8 mm.


34

2) The cement used in this research was Ordinary Portland Cement produced in

Turkey; the properties of cement met the requirements of ASTM C 150

specifications.

3) Drinking water was used in NSC mixing and curing, no superplasticizers were

added to the mix.

NSC Mixing Proportions 3.5.2.

The absolute volume method recommended by the ACI 211.1 committee was used

to compute the quantities of concrete materials required for the NSC mix. Table ‎3-2

shows the NSC mixing proportions.

Table ‎3-2: NSC Mixing Proportions.

Four concrete standard cylinders were casted and cured in water until being tested at 28

days.

Properties of Reinforcement Steel 3.5.3.

The UC, MC reference columns and G1, G2, G3 column cores were reinforced with two

types of steel reinforcing bars. High steel tensile strength of 420MPa was used as a

longitudinal steel reinforcement, while steel stirrups having steel tensile strength of

280MPa was used. Figure ‎3-4 shows the testing machine at the IUG Soil and Materials

Laboratory.

Figure ‎3-4: Main Rebar Tension Test.

Tests were carried out for each bar size, three steel specimens of 10mm diameter bar

and 300mm long were prepared, as well as preparing another three steel specimens of

4mm diameter bar and 250mm long. All steel samples were obtained from randomly

Material Qty/m3

Coarse Aggregate 1316.8 kg

Fine Aggregate (Sand) 658.4 kg

Cement 300 kg

Water 165 liters


35

chosen bars. Table ‎3-3 shows the obtained testing results of main longitudinal steel

reinforcement and the transverse steel stirrups.

Table ‎3-3: Steel Reinforcement Testing Results.

Bar Type Nominal

Diameter (mm)

Actual

Diameter

(mm)

Yield Stress

(MPa)

Ultimate Tensile

Strength

(MPa)

% Age

Elongation

Plain 4 4 280 365.8 26

Deformed 10 10 420 562.8 16

Reinforcement Details 3.5.4.

The longitudinal steel reinforcement of 4Ø10 mm and steel stirrups of 4Ø4 mm were

used for the UC, MC reference columns and the G1, G2, G3 column cores. The overall

length of the steel cages was 250mm, with steel stirrups spaced at 60mm.

The concrete cover was 10mm for all column specimens. Figure ‎3-5 shows the

geometry and steel detailing of the column cores.

Figure ‎3-5: Geometry and Steel Details of Column Core.

Mixing Procedures 3.5.5.

The required amounts of the NSC constituent materials were weighed accurately. The

aggregates were mixed homogeneously with the cement paste using a tilting revolving

drum mixer as shown in Figure ‎3-6. The mixer has an arrangement of interior fixed

blades to ensure end to end exchange of material during mixing, having the advantage


36

of a quick and clean discharge. The mixing procedures were included in the following

steps:

1) Place all dry materials (cement, sand and coarse aggregate) in the mixer, and mix

for 2 minutes.

2) Add the water to the dry materials, slowly for 2 minutes.

3) Continue mixing as the NSC changes from a dry state to a thick paste, all mixing

procedures were carried out at room temperature of about (20-25°c).

4) The mixer was stopped after completing mixing and turned up with its end right

down and the fresh homogeneous concrete was poured into a clean plastic pan.

5) Casting NSC mix in the timber moulds of column specimen’s and standard test

cylinder was completed within 20 minutes.

Figure ‎3-6: Handling Fresh NSC Mix from Mixing Drum.

Casting of NSC 3.5.6.

The fresh concrete was casted in timber moulds which were manufactured by clean and

smooth surface timber. The surface was coated with oil before casting to easily separate

and unmould the hardened column specimens as shown in Figure ‎3-7. The prepared

steel cages were located in their proper position into the timber moulds. Concrete chairs

were fixed on the column specimens’ four faces to maintain the design concrete cover.

Figure ‎3-7: Oiling and Casting Timber Moulds.


37

The concrete was placed in the timber moulds and the surface was smoothed by

trowelling. Four standard test cylinders having a height of 300mm and a diameter of

150mm were used in compliance with ASTM C470 standards. The four standard test

cylinders were casted from the same batch of NSC mix and compacted mechanically

using a hand tamping rod to prevent segregation and honeycombing.

Curing of NSC 3.5.7.

After concreting was completed, the concrete was struck off level with the top edge of

the moulds with minimum disturbance. The sides of the moulds were stripped away

after being left for 24 hours.

The UC and MC reference columns were submerged in curing water basin for 28 days.

Whereas the G1, G2 and G3 column cores were submerged in curing water basin for at

least 7 days before being jacketed.

The four standard test cylinders were also submerged in curing water basin for 28 days

to be tested on the same day of testing UC and MC reference columns.

3.6. Preparation of the Jacket

Three jacketing styles were applied on three groups of column cores G1, G2 and G3;

G1 group represented 9 column cores jacketed by Fibrous UHPSCC without placing

steel reinforcement cage in the jacket. G2 group represented 9 column cores jacketed by

Non-Fibrous UHPSCC and steel reinforcement cage was placed in jacket. The G3 group

represented 9 column cores jacketed by Fibrous UHPSCC and steel reinforcement cage

was placed in jacket.

Properties of Fibrous UHPSCC 3.6.1.

In this research, UHPSCC was used as a jacketing material depending on the

ingredients of ordinary Portland cement, grey silica fume, crushed quartz, quartz

powder, basalt aggregates, and superplasticizer from a recognized manufacturer.

Proportions of the constituent materials were chosen carefully in order to optimize the

packing density of the mix as discussed in the followings.

Aggregates 3.6.1.1.

Aggregate is relatively inexpensive and strong material for concrete. It is treated

customarily as inert filler. The aggregate maximum size and strength were the primary

concerns in designing the UHPSCC mix.

Providing self-compacting concrete requires the non-use of large aggregates. While

producing UHPSCC requires the selection of very strong aggregate (crushed basalt) of

rough texture, and a nominal size ranges from 2 to 5 mm. The quartz sand (fine

aggregate) ranges from 0.3 to 0.8 mm and the quartz powder (micro fine aggregate)


38

ranges from 0 to 10 µm. Figure ‎3-8 shows the appearance of aggregates used in

preparing the UHPSCC mix.

Figure ‎3-8: The Aggregates Used in UHPSCC Mix.

It was important to use clean aggregates, as silt or clay impurities may reduce the

bonding strength between cement and aggregates, requiring extra amount of water.

Cement 3.6.1.2.

Ordinary Portland cement was used with different quantities per cubic meter. Cement

paste was considered to be the binder that holds the aggregate (coarse, fine, micron fine)

together and reacted with mineral materials in hardened mass. The property of

UHPSCC depended on the quantity and the quality of used cement.

As cement is the most active component of UHPSCC and usually has the greatest

unit cost, its selection and proper use was important in obtaining most economical

desired properties of UHPSCC.

In this research, ordinary Turkish Portland Cement CEM I 42.5R was used and satisfied

the ASTM C 150 requirements. The results of physical and mechanical analyses of the

cements were summarized in Table ‎3-4 along with the requirements of relevant ASTM

specifications for comparison purposes.

Table ‎3-4: Cement Properties Based on Manufacturer Sheet.‎[37]

Test Type Ordinary Portland Cement

Results ASTM C 150

Setting time (Vicat Test) hr, min Initial 1 hr – 30 min More than 60 min

Final 4 hrs – 40 min Less than 6 hrs 15 min

Mortar Compressive Strength (MPa)

3 Days 25.7MPa Min. 12MPa

7 Days 36.9MPa Min. 19MPa

8Days 53.4MPa No limit

Fineness (cm2/gm) 3006 Min. 2800

Water Demand 27.5 % No limit

Mixing Water 3.6.1.3.

Clean and free from impurities drinking water was used for curing purposes. The source

of water was available at IUG Soil and Materials Laboratory. Keeping in mind the

principle of using concrete mixing water that says, if you can drink it you can make

concrete with it.


39

Forta-Ferro Polypropylene Fibers (FFP) 3.6.1.4.

FFP Fibers is microfibers produced by Forta Company. In this research, FFP fibers were

used as discussed in previous chapter to produce the Fibrous UHPSCC mix. Figure ‎3-9

shows the appearance of FFP fibers.

Figure ‎3-9: Forta-Ferro Polypropylene Fibers.‎[4]

FFP fibers provided a low dose, steel free solution for thin and slim concrete elements.

Its length and strength makes it ideal for thin sections and for increasing the ductility

and flexural strength of the designed Fibrous UHPSCC mix [35, 36 and 37]. Table ‎3-5

presents the FFP physical properties.‎

Table ‎3-5: Physical Properties of Forta Ferro Polypropylene Fibers.‎[4]

Materials: Virgin

Copolymer/Polypropylene

Form: Monofilament/Fibrillated Fiber System

Color: Gray

Acid/Alkali Resistance: Excellent

Specific Gravity: 0.91

Tensile Strength: 570-660 MPa

Length: 54mm, 38mm

Absorption: Nil

Compliance: ASTM C-1116

Superplasticizer 3.6.1.5.

The superplasticizer is a high range water reducer, which is very important in the case

of low w/c ratio to improve the workability, flowability and self-compactability of

UHPSCC. The superplasticizer has the ability to improve the shrinkage, creep behavior

and water impermeability if it is satisfying ASTM-C-494 specifications.

Sikament 163M superplasticizer was used in this research, it is produced by SIKA

Company, see Figure ‎3-10. The properties and specifications of Sikament 163M are

shown in Table ‎3-6.

Table ‎3-6: Sikament 163M Technical Data.‎[37]

Type Property

Appearance Brown Liquid

Density 1.200 ± 0.005 Kg/l

PH Value 7.5

Toxicity Non-Toxic

Three tests (Slump flow, V-funnel and L-shape) were carried to ensure the SCC

behavior of the UHPSCC mix using Sikament 163M superplasticizer at the IUG Soil

and Materials Laboratory.


40

Figure ‎3-10: Sikament 163M Superplasticizer.

The results obtained were satisfying the fresh properties standards developed by the

European Guidelines of self-compacting concrete (EFNARC) as presented in Table ‎3-7.

Table ‎3-7: Self-Compacting Properties of UHPSCC Mix.

Method Unit Obtained Results

Slump flow (Abram Cone) mm 563

V- funnel S 9.7

L – Box (h2/h1) - 0.82

Silica Fume 3.6.1.6.

Silica fume is a byproduct resulting from the reduction of high-purity quartz with coal

or coke and wood chips in an electric arc furnace during the production of silicon metal

or ferrosilicon alloys.

The silica fume which condenses from the gases escaping from the furnaces has a very

high content of amorphous silicon dioxide and consists of very fine spherical particles

(ACI 548.6R-96). Figure ‎3-11 shows the silica fume appearance.

Figure ‎3-11: Silica Fume Appearance

Sika-Fume was used in this research as a silica fume produced by SIKA Company.

Table ‎3-8 presents the technical data of the Sika-Fume.

Table ‎3-8: Sika-Fume Properties.‎[37]

Type Property

Appearance Grey powder

Specific gravity 2.20

Chloride content Nil

Toxicity Non-toxic


41

Mixing Proportions of Fibrous and Non-Fibrous UHPSCC 3.6.2.

Two mixes of Fibrous and Non-Fibrous UHPSCC were made depending on the

ingredients proportions detailed in Table ‎3-9. The UHPSCC mix was designed to obtain

targeted standard cylinder compressive strength of about 125MPa.

Table ‎3-9: Mixing Proportions of Fibrous UHPSCC.‎[35 and 37]

Material Name Kg/m3 Proportions/Cement Weight

Cement Content 950 1.0

Water 332.5 0.35

Silica Fume 285 0.30

Basalt Content 1425 1.50

Quartz Powder 327.15 0.34

Quartz Sand 622.85 0.66

Superplasticizer 33.25 0.035

Forta-Ferro Polypropylene Fibers 13.65 1.5% by volume of mix

G1and G3 column cores were strengthened using Fibrous UHPSCC jacket, while G2

column cores were strengthened using Non-Fibrous UHPSCC (no PPF fibers was added

to the mix) as detailed in Table ‎3-10.

Table ‎3-10: Details of G1, G2 and G3 Jacketed Column Specimens.

# Group

Name Not.

Overall Jacketed

Column Section, mm

Jacket

Thickness, mm

Jacketing

Material

Jacket Steel

Reinforcement

1 G1 Column

Cores

G1-25 150×150 25 Fibrous

UHPSCC

2 G1-30 160×160 30 Un-reinforced

3 G1-35 170×170 35

4 G2 Column

Cores

G2-25 150×150 25 Non-Fibrous

UHPSCC

5 G2-30 160×160 30 Reinforced

6 G2-35 170×170 35

7 G3 Column

Cores

G3-25 150×150 25 Fibrous

UHPSCC

8 G3-30 160×160 30 Reinforced

9 G3-35 170×170 35

Reinforcement Details 3.6.3.

Two diameters of steel bars were used to prepare the jacket steel cages, main steel

reinforcement of 4Ø10 mm and steel stirrups of 4Ø4 mm. The properties of the jacket

steel cages were similar to that of reference and column cores steel cages. Steel cages

were located for only two groups of column cores G2 and G3, while G1 column cores

were jacketed without jacket steel cages, as shown before in Table ‎3-10. Shear

connectors were used with the three groups of column cores G1, G2 and G3 for the

purpose of interface bonding. The spacing was carefully maintained between old

concrete and the jacket steel cages with external concrete cover not less than 10mm.

The following points summarize the carried out experimental steps of jacketing:

1) 4Ø10mm main steel reinforcing bars were used at the four corners of column cores,

having a length of about 250mm and a diameter of 10mm. Figure ‎3-12 shows the

geometry and steel detailing of the G1-25, G2-25 and G3-25.

2) 4Ø4mm transverse steel stirrups were used and fixed to the longitudinal steel bars

(not welded) with a vertical spacing of 60mm.


42

3) Mechanical bonding technique (post installed shear connectors) was applied to

bond the old concrete to the new concrete.

4) Concrete substrate was not roughened in order to eliminate the influence of friction

when assessing the effectiveness of shear connectors.

5) Drilling machine with 6mm diameter drilling bit was used to perforate a hole

having a diameter of 6mm and a depth of 25mm based on ASTM A 307 standards.

6) Drilled holes were filled with Sikadur 31CF bonding material which is supplied

from SIKA Company to confirm the good bonding between shear connectors and

old concrete.

7) The L-shape shear connectors were used having a diameter of 4mm and a length of

40mm. 25mm long of the shear connector was inserted in the drilled hole and the

remaining length of 15mm was not inserted.

8) Four shear connectors were fixed with the jacket steel cage in a staggered

horizontal alignment on every column face with a vertical spacing of 60mm, and

edge distance of 30mm based on ASTM A 307 standards, see Figure ‎3-13.

Figure ‎3-12: Geometry and Steel Details of G1-25, G2-25 and G3-25.


43

Figure ‎3-13: Shear Connectors and Bonding Agent.

Mixing Procedures 3.6.4.

Fibrous and Non-Fibrous UHPSCC mixes were made at IUG Soil and Material

laboratory. All required amounts of constituent materials were weighed accurately and

mixed properly to produce homogeneous concrete mass using the same tilting revolving

drum mixer. The mixing procedures were included in the following steps:

1) Add 40 % of superplasticizer to the mixing water.

2) Place all dry materials (cement, silica fume, crushed quartz and aggregate) with

50% of the FFP fibers in the drum mixer, and mix for minimum 2 minutes.

3) Place the mixing water (with 40% of superplasticizer) to the dry materials, slowly

for 2 minutes.

4) Wait for a minute while the drum is revolving then add the remaining

superplasticizer to the batch for 30 seconds.

5) Continue mixing for 5 minutes and add the remaining 50% of the FFP fibers,

noting that the Fibrous UHPSCC start changing from dry state to a thick paste.

6) The mixer was stopped after completing mixing, turned up with its end right

down, and the fresh homogeneous concrete was poured into a clean plastic pan.

7) The mix casting should be completed within not more than 20 minutes.

All the above mentioned steps were repeated again to prepare the Non-Fibrous

UHPSCC mix.

Casting of UHPSCC 3.6.5.

The fresh Fibrous UHPSCC was casted in the timber moulds of the G1 and G3 column

cores. Timber moulds were manufactured with very accurate dimensions based on the

required jacket thickness, and made of hard, clean and smooth surface timber. The

surface was coated with oil before casting to easily separate and unmould hardened


44

column specimens. The column cores with reinforcement steel cages were directly

located into the timber moulds in a proper position and supported on concrete chairs to

maintain a concrete cover of 10mm as shown in Figure ‎3-14.

After the Fibrous UHPSCC was casted in the timber moulds, the surface was smoothed

by troweling. Four standard test cylinders having a height of 300mm and a diameter of

150mm were used in compliance with ASTM C470 standards. The four standard test

cylinders were casted from the same batch of UHPSCC mix without manual

compaction (as it is self-compacting concrete).

All the above mentions steps were repeated again to cast the Non-Fibrous UHPSCC for

the group G2 of column cores and the corresponding four standard test cylinders.

Curing of UHPSCC 3.6.6.

After concreting was completed, the concrete was struck off level with the top edge of

the moulds with minimum disturbance. The sides of the moulds were stripped away

after being left for 24 hours.

The G1, G2 and G3 jacketed column specimens were submerged in curing water basin

for 28 days. Eight standard test cylinders were cast of Fibrous and Non-Fibrous

UHPSCC mixes (four cylinders for each mix) and submerged in curing water basin for

28 days, see Figure ‎3-14.

Figure ‎3-14: Column Cores Located in Timber Moulds before and after Casting.

3.7. Testing of Column Specimens

The UC, MC reference columns and the G1, G2 and G3 jacketed column specimens

were tested experimentally using high capacity compression testing machine (supplied

by Matest Company for material testing and equipment having a code number of

C109N), ‎[40]. The machine configuration was changed to moduelastic system to enable

testing compressive strength versus the axial strain in compliance with ASTM C470 as

discussed in the following:


45

The Ultimate Load Carrying Capacity of Column Specimens 3.7.1.

After ending the curing period, the UC, MC reference columns and G1, G2, G3 jacketed

column specimens were kept in dry place for 10 to15 minutes to attain surface dry

condition. Loose sand grains or incrustations were removed from contact faces with

testing machine platens.

The column specimens were then located carefully in the testing machine in order to

ensure the vertical concentricity (uniaxial) of the applied compressive load. Thereafter,

test was carried out by the hydraulic machine with 3000KN compression testing

capacity.

All column specimens were tested under monotonically small loading rate of about 6

KN/sec and a starting load of about 20 KN. The load was applied vertically at the top

and bottom of the column specimens until failure and compression readings were

collected.

The Longitudinal Axial Strain of Column Specimens 3.7.2.

Longitudinal axial strains of UC, MC reference columns and G1, G2, G3 jacketed

column specimens were measured using the same compression testing machine. Three

strain dial gauges (also called transducers) within accuracy of about 0.00254 mm were

fixed at the mid height of the column three faces prior to testing as shown Figure ‎3-15.

At each increment of 6 KN axial compression load, readings of longitudinal axial strain

were recorded using the machine data acquisition system.

Figure ‎3-15: The Compression Testing Machine

CHAPTER 4RESULTS & DISCUSSION

CHAPTER 4 RESULTS & DISCUSSION

47

4.1. Introduction

This chapter discussed the results of the carried out tests on the RC column specimens

and standard test cylinders, to investigate the impact of strengthening RC column

specimens with Fibrous UHPSCC jacket. A comparative study was made between UC,

MC reference columns and the three groups of jacketed column specimens G1, G2 and

G3. In addition, the effectiveness of every jacketing style was investigated in terms of

ultimate load carrying capacity and longitudinal axial strain.

4.2. NSC Compressive Strength

The compressive strength of the normal strength concrete (NSC) was obtained by

testing four standard test cylinders (300 mm high and 150mm diameter) at 28 days. The

test results are shown in Table ‎4-1.

Table ‎4-1: Compression Test Results of NSC.

Mix Type Notification Cylinder Compressive Strength, MPa

Normal strength

concrete (NSC)

S1 21.1

S2 21.8

S3 24.3

S4 21.3

Average 22.2

Table ‎4-1 shows the average compressive strength of the four tested standard cylinders

that almost equals the targeted NSC cylinder compressive strength of 20MPa. The

experimentally obtained results represented the realistic concrete compressive strength

after being damaged throughout its working life, and thus required strengthening.

4.3. UHPSCC Compressive Strength

The Compressive strengths of Fibrous and Non-Fibrous UHPSCC were obtained by

testing eight standard test cylinders (300 mm high and 150mm diameter) at 28 days.

The test results are presented in Table ‎4-2.

Table ‎4-2: Compression Test Results of Fibrous and Non-Fibrous UHPSCC.

Mix Type Notification Cylinder Compressive Strength, MPa

Fibrous UHPSCC

Mix

S1 118.5

S2 118.0

S3 107.3

S4 112.6

Average 114.1

Non-Fibrous

UHPSCC Mix

S1 104.5

S2 99.7

S3 101.4

S4 95.4

Average 100.3

Table ‎4-2 revealed that the average compressive strength of Fibrous and Non-Fibrous

UHPSCC are 114.1MPa and 100.3MPa respectively. The obtained result of Fibrous

UHPSCC compressive strength was almost similar to the targeted compressive strength

of 125MPa.


48

4.4. UC Reference Column

The UC reference column was casted using NSC mix to act as a reference unjacketed

column specimen, and to obtain the column core ultimate load carrying capacity before

being jacketed. A uniaxial monotonic compression load was applied on the UC

reference column to obtain the average ultimate load carrying capacity and the

longitudinal axial strain.

Results of UC Ultimate Load Carrying Capacity 4.4.1.

The ultimate load carrying capacity of the three samples (UC-S1, UC-S2, and UC-S3)

of UC reference column was obtained at 28 days, as presented in Table ‎4-3.

Table ‎4-3: UC Ultimate Load Carrying Capacity.

Notification Pu (KN) Column Sectional Area (cm2) Calculated Pu (KN)

UC-S1 291.6

All UC samples have column

sectional area of 100 cm2

179.5 UC-S2 296.7

UC-S3 294.2

Average 294.2

Table ‎4-3 shows that the average ultimate load carrying capacity of UC reference

column is 294.2 KN, and the calculated nominal load carrying capacity of a

corresponding column using ACI 318-11 is 179.5 KN. The difference between the

experimental Pu and the calculated nominal Pu can be attributed to the factor of safety

provided by ACI code for designing the RC short columns.

The results showed that the UC reference column has satisfied the code requirements in

representing column cores before being jacketed. Figure ‎4-1 shows the failure modes of

UC reference column.

Figure ‎4-1: Failure Pattern of UC Reference Column.

Results of UC Longitudinal Axial Strain 4.4.2.

The axial strain values were recorded versus load values using the three axial strain

transducers fixed at the mid height of the column three faces. Load-strain diagrams were

plotted for the three samples of UC reference column as shown in Figure ‎4-2.


49

Figure ‎4-3 shows the average load-strain diagram of UC reference column, with a

maximum axial strain of 0.0032 at rupture point.

Figure ‎4-2: Load-Strain Diagram of UC Reference Columns.

Figure ‎4-3: Average Load-Strain Diagram of UC Reference Column.

4.5. MC Reference Columns

The MC reference columns were monolithically casted using NSC mix to act as

reference column specimens. MC1, MC2 and MC3 reference columns were subjected to

vertical uniaxial monotonic compression load to obtain the average ultimate load

carrying capacity and the longitudinal axial strain.

Results of MC Ultimate Load Carrying Capacity 4.5.1.

The ultimate load carrying capacity of the three samples (S1, S2 and S3) of MC

reference columns were obtained at 28 days as presented in Table ‎4-4.

0

50

100

150

200

250

300

350

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC-S1

UC-S2

UC-S3

0

50

100

150

200

250

300

350

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain


50

Table ‎4-4: MC Ultimate Load Carrying Capacity.

Notification Pu (KN) Column Sectional Area (cm2) Calculated Pu (KN)

MC1-S1 514.5

225 311.6 MC1-S2 530.0

MC1-S3 538.9

Average 527.8

MC2-S1 600.9

256 344.4 MC2-S2 559.0

MC2-S3 617.8

Average 592.6

MC3-S1 672.0

289 379.2 MC3-S2 663.6

MC3-S3 652.2

Average 662.6

Table ‎4-4 shows that the average ultimate load carrying capacity of MC1, MC2 and

MC3 reference columns are 527.8, 592.6 and 662.6KN respectively. While the

calculated nominal load carrying capacity of MC1, MC2 and MC3 using ACI318-11 are

311.6, 344.4 and 379.2KN respectively. The difference between the experimental Pu and

the calculated nominal Pu can be attributed to the factor of safety provided by ACI code

for designing the RC short columns.

Figure ‎4-4 shows the obtained ultimate load carrying capacity of UC, MC1, MC2 and

MC3 with respect to the column cross sectional area. The figure revealed that there is a

significant increase of 79.4%, 101.4% and 125.2% in ultimate load carrying capacity of

MC1, MC2 and MC3 reference columns with respect to UC reference column

respectively.

This can be attributed to the higher column cross sectional area of MC1, MC2 and MC3

reference columns with an increase of 125,156 and 189 cm2 compared to UC reference

column respectively.

Figure ‎4-4: Ultimate Load Carrying Capacity of UC and MC Reference Columns.

UC

MC

1 MC

2

MC

3

0

100

200

300

400

500

600

700

100 225 256 289

Co

lum

n C

apac

ity

(KN

)

Column Sectiona Area (cm2)


51

Results of MC Longitudinal Axial Strain 4.5.2.

The axial strain values were recorded versus load values using the three axial strain

transducers fixed at the mid height of the column three faces, load-strain diagrams were

plotted for the three samples of every MC1, MC2 and MC3 reference column as shown

from Figure ‎4-5 to Figure ‎4-10.

Figure ‎4-5: Load-Strain Diagram of MC1 Reference Column.

Figure ‎4-6: Average Load-Strain Diagram of MC1 Reference Column.


0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

MC1-S1

MC1-S2

MC1-S3

0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

MC2-S1

MC2-S2

MC2-S3


52




0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

MC3-S1MC3-S2MC3-S3

0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain


53

Figure ‎4-11 presents the obtained load strain diagrams of UC, MC1, MC2 and MC3

column specimens. The figure also shows that the load strain relations are nearly linear

up to one third the ultimate load carrying capacity, beyond which the curves became

nonlinear.

The UC, MC1, MC2 and MC3 reference columns reached their ultimate load carrying

capacities at axial strains of about 0.002, having almost equal axial strains at rupture

points of 0.0032, 0.0035, 0.0033 and 0.0031 respectively. This can be attributed to the

fact that they have similar steel reinforcement and were made of similar NSC mix.

Figure ‎4-11: Load-Strain Diagrams of UC, MC1, MC2 and MC3 Reference Columns.

4.6. G1 Jacketed Column Specimens

The G1 jacketed column specimens namely G1-25, G1-30 and G1-35 were consisted of

nine column cores strengthened using a jacket made of Fibrous UHPSCC and without

steel reinforcement cages in jacket. Shear connectors were used to mechanically bond

between column cores and its jacket. The results of G1 ultimate load carrying capacity

were studied in terms of jacket thickness, and compared with the corresponding UC and

MC reference columns. Longitudinal axial strains and failure patterns were also

obtained and compared with that of UC and MC reference columns.

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Ultimate Load 4.6.1.

Carrying Capacity

Several jacket thicknesses namely 25, 30 and 35 mm gave an obvious increase in the

ultimate load carrying capacity. The overall composite cross sections of G1 jacketed

column specimens were made of two different concrete mixes; the column cores were

made of NSC mix and the outer jackets were made of Fibrous UHPSCC mix. Table ‎4-5

presents the average ultimate load carrying capacity of G1-25, G1-30 and G1-35.

0

100

200

300

400

500

600

700

0 0.0005 0.001 0.0015 0.002 0.0025 0.003 0.0035 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC1

MC2

MC3


54

Table ‎4-5: G1 Ultimate Load Carrying Capacity.

Notification Pu (KN) Overall Composite

Area (cm2)

Jacket Area

(cm2)

Column Core

Area (cm2)

G1-25-S1 1026.5

225 125

All Specimens

have column cores

area of 100 cm2

G1-25-S2 1064.2

G1-25-S3 1078.2

Average 1056.3

G1-30-S2 1226.1

256 156 G1-30-S2 1217.2

G1-30-S2 1250.3

Average 1231.2

G1-35-S3 1517.0

289 189 G1-35-S3 1535.9

G1-35-S3 1509.9

Average 1520.9

Figure ‎4-12 shows the effect of jacket thicknesses on G1 ultimate load carrying

capacity. The column cores were casted using NSC mix with unchanged cross section

of 100×100mm, thus the increase in cross sectional area was obtained by applying

several jacket thicknesses.

The ratios of jacket area of G1-30/G1-25 and G1-35/G1-25 equaled 1.25 and 1.51

respectively, while the corresponding ratios of ultimate load carrying capacity equaled

1.16 and 1.44 respectively. That has revealed the almost direct proportional relation

between jacket thickness and ultimate load carrying capacity of G1 jacketed column

specimens.

Figure ‎4-12: G1 Ultimate Load Carrying Capacity.

The results obtained were in agreement with that obtained by Abdelrahman ‎[26] who

found that for regional strengthening, the ultimate load of strengthened columns was

less than the increase in the cross sectional area. But equal to the increase in the cross

sectional area if column entire length was jacketed.

In particular, jacket thickness is controlled by the required concrete covers in case of

traditional concrete jacketing. This often leads to thicknesses higher than 60 to100 mm

G1

-25

G1

-30

G1

-35

0

200

400

600

800

1000

1200

1400

1600

1800

225 256 289

Co

lum

n C

apac

ity

(KN

)

Column Composite Sectional Area (cm2)


55

and thus an increase in the overall column sectional area. This was totally avoided by

applying small jacket thicknesses of Fibrous UHPSCC.

Table ‎4-6 indicates that the G1-25, G1-30 and G1-35 jacketed column specimens

showed a huge increase in ultimate load carrying capacity 3.6, 4.2 and 5.2 times higher

than the UC reference column respectively. Table ‎4-6 also presents that G1-25, G1-30

and G1-35 gained high increase in ultimate load carrying capacity of 2.0, 2.1 and 2.3

times higher than the corresponding MC reference columns respectively.

Table ‎4-6: Increase in G1 Ultimate Load Carrying Capacity with Respect to UC and MC.

A B C C/A C/B

UC, Pu (KN) MC, Pu (KN) G1, Pu (KN)

294.2

MC1 527.8 G1-25 1056.3 3.6 2.0

MC2 592.6 G1-30 1231.2 4.2 2.1

MC3 662.6 G1-35 1520.9 5.2 2.3

Figure ‎4-14 shows the ultimate load carrying capacity of G1-25, G1-30 and G1-35

jacketed column specimens plotted with the UC and MC reference columns.

It was noticed that applying G1 jacketing style made of Fibrous UHPSCC unreinforced

jacket has provided a high improvement in the compression performance of the

composite section of G1-25, G1-30 and G1-35 jacketed column specimens with an

increment of about 100% with respect to corresponding MC reference columns.

Figure ‎4-13: G1 Ultimate Load Carrying Capacity with Respect to UC and MC.

The results obtained almost matched that obtained by Meda et al. ‎[23] who

strengthened a concrete column of cross section (300×300mm) with a high

performance fiber reinforced concrete jacket of 30mm jacket thickness. He found that

the ultimate capacity of the jacketed columns were more than 4 times the unjacketed

columns.

MC

1

MC

2

MC

3

UC

G1

-25

G1

-30

G1

-35

0

200

400

600

800

1000

1200

1400

1600

1800

100 225 256 289

Co

lum

n C

apac

ity

(KN

)



56

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Longitudinal 4.6.2.

Axial Strain

The axial strain values were recorded versus load values. The load-strain diagrams were

plotted for the three samples S1, S2 and S3 of the G1-25, G1-30 and G1-35 jacketed

column specimens. The average load-strain diagrams were also obtained and plotted as

shown from Figure ‎4-14 to Figure ‎4-19.

Figure ‎4-14: Load-Strain Diagram of G1-25 Jacketed Column Specimens.

Figure ‎4-15: Average Load-Strain Diagram of G1-25 Jacketed Column Specimens.


0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G1-25-S1

G1-25-S2

G1-25-S3

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G1-30-S1

G1-30-S2

G1-30-S3


57




0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G1-35-S1

G1-35-S2

G1-35-S3

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain


58

Figure ‎4-20 shows that the maximum axial strains of G1-25, G1-30 and G1-35 at failure

were 0.007, 0.006 and 0.0066 respectively. It was noticed that a significant increase in

maximum axial strains of G1-25, G1-30 and G1-35 was obtained in spite of using a

brittle and high strength UHPSCC as jacketing material. That can be attributed to the

presence of 1.5% Forta-Ferro Polypropylene fibers (FFP fibers) by concrete volume

which improved the ductility performance of the column section.

Figure ‎4-20: Average Load-Strain Diagram of G1-25, G1-30 and G1-35

The maximum measured axial strains (axial strain at rupture) of UC, MC reference

columns and G1-25, G1-30 and G1-35 jacketed column specimens were compared in

Table ‎4-7.

It can be seen from Table ‎4-7 that G1 jacketed column specimens have gained

significant increase in the longitudinal axial strain at rupture with respect to UC and MC

reference columns. The longitudinal axial strains of G1 jacketed column specimens

were 2 times the axial strains of UC and MC reference columns.

Table ‎4-7: Increase in G1 Maximum Longitudinal Axial Strain with Respect to UC and MC.

A B C

C/A C/B UC, Axial Strain @

Failure

MC, Axial Strain

@ Failure

G1, Axial Strain

@ Failure

0.0032

MC1 0.0035 G1-25 0.0070 2.2 2.0

MC2 0.0032 G1-30 0.0066 2.1 2.1

MC3 0.0031 G1-35 0.0066 2.1 2.1

In order to study the improvement in ductility, the G1-25, G1-30 and G1-35 axial strain

curves were drawn together with the corresponding axial strain curves of UC and MC

reference columns as shown in Figure ‎4-21.

The load strain curves of G1 jacketed column specimens are nearly linear up to one

third the ultimate load carrying capacity but with steeper slopes than that of MC and UC

axial strain curves, after that the curves became nonlinear. That means that the modulus

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G1-25

G1-30

G1-35


59

of elasticity of G1 jacketed column specimens is much higher than that of UC and MC

reference columns.

Figure ‎4-21: Average Load-Strain Diagrams of G1-25, G1-30, G1-35 with Respect to UC and MC.

Figure ‎4-21 also shows that the G1 jacketed column specimens reached their ultimate

load carrying capacity at nearly axial strains of 0.0034 regardless of their ultimate

capacities, whereas, UC and MC reference columns reached their ultimate load carrying

capacity at axial strains of 0.002.

This can be attributed to the application of the Fibrous UHPSCC a jacketing material,

which has improved the ductility performance of the G1 jacketed column sections and

increased the values of axial strains at ultimate load carrying capacity.

It is worth mentioning that the significant enhancement in ductility was obtained

without adding steel reinforcement cages in the jacket, just adopting Fibrous UHPSCC

jacket. The addition of FFP fibers has significantly improved the ductility and the

ability to sustain extra longitudinal axial strains before breaking. The Fibrous UHPSCC

jacket has imposed passive confinement on the four jacketed sides bonded mechanically

by shear connectors only, without any extra treatment of the old concrete surfaces.

The results obtained in this research did not match that obtained by Ersoy et al. ‎[27]

who found that the axial strains of the jacketed columns at failure did not exceed 0.002,

which was attributed to the fact that the jacketing material used in his study has low

ductile properties, unlike the Fibrous UHPSCC.

Effect of Fibrous UHPSCC Unreinforced Jacketing on G1 Failure Pattern 4.6.3.

The UC, MC reference columns and the G1 jacketed column specimens were all tested

until reaching the ultimate load. The failure was initiated by vertical hairline cracks at

the middle part of the UC and MC reference columns. The vertical hairline cracks were

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC1

MC2

MC3

G1-25

G1-30

G1-35


60

initiated at the middle portion of the G1 jacketed column specimens and became visible

at 90% to 95% of the ultimate load. The number and width of these cracks increased

with the increase in the axial load until the specimen reached its failure load.

The G1 jacketed column specimens exhibited a gradual ductile failure mode unlike the

UC and MC reference columns, which showed sudden brittle failure mode. The failure

of G1 jacketed column specimens was mainly caused by the failure of the jacket at the

corners of the specimen that resulted in the separation and bulging of the jacketing layer

away from the specimen.

Figures ‎4-22, 4-23 and ‎4-24 show the typical failure modes of the UC, MC reference

columns and G1 jacketed column specimens. Stirrups rupture at the mid height of MC

reference columns was noticed.

The G1 jacketed column specimens have shown warning signs before failure clearer

than that of UC and MC reference columns. It is worth mentioning that such increases

were almost due to the confinement offered by the application of Fibrous UHPSCC

jacket which improved the ductile behavior of the jacketed column specimen.

`

Figure ‎4-22: Failure Pattern of UC Reference Column.

Figure ‎4-23: Failure Pattern of MC Reference Columns.


61

Figure ‎4-24: Failure Pattern of G1 Jacketed Column Specimens.



nine column cores strengthened using a jacket made of Non-Fibrous UHPSCC with

steel reinforcement cages in the jacket. Shear connectors were used to mechanically

bond between column cores and its jacket.

The results of G2 ultimate load carrying capacity were investigated in terms of jacket

thickness, and compared with the corresponding UC and MC reference columns. The

G2 longitudinal axial strains and failure patterns were also obtained and compared with

that of UC and MC reference columns.

Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 Ultimate 4.7.1.

Load Carrying Capacity

The several jacket thicknesses namely 25, 30 and 35 mm gave an obvious increase in

the ultimate load carrying capacity. The overall composite cross sections of G2 jacketed

column specimens were made of two different concrete mixes; column cores were made

of NSC mix and the outer jackets were made of Non-Fibrous UHPSCC mix. Table ‎4-8

presents the average ultimate load carrying capacity of G2-25, G2-30 and G2-35.



Area (cm2)

Jacket Area

(cm2)

Column Core

Area (cm2)

G2-25-S1 1015.6

225 125

All Specimens

have column

cores area of 100

cm2

G2-25-S1 1048.5

G2-25-S1 1023.8

Average 1029.3

G2-30-S1 1211.9

256 156 G2-30-S1 1225.9

G2-30-S1 1256.3

Average 1231.3

G2-35-S1 1438.1

289 189 G2-35-S1 1281.0

G2-35-S1 1489.3

Average 1402.8


62




several jacket thicknesses.


respectively, while the corresponding ratios of ultimate load carrying capacity equaled

1.2 and 1.36 respectively. That has revealed the almost direct proportional relation


specimens. The results obtained were in agreement with that of G1 and matched the

results obtained by Abdelrahman ‎[26] and Allam ‎[22].


Table ‎4-9 shows that G2-25, G2-30 and G2-35 jacketed column specimens have gained

significant increase in ultimate load carrying capacity 3.5, 4.2 and 4.8 times higher than

the UC reference column respectively.

The results obtained in this research was in agreement with that obtained by Meda et

al ‎[23] who concluded that the carrying capacity of the jacketed columns was 4 times

higher than that of unjacketed one. Meda et al. has adopted 30mm jacket thickness to a

column core cross section of 300×300mm using ultra high performance concrete.

Table ‎4-9 also presents that G2-25, G2-30 and G2-35 have doubled its ultimate load

carrying capacity compared to the corresponding MC reference columns. Unlike the

results obtained by Ersoy et al. ‎[27] who found that the carrying capacity of the

jacketed column specimens reached from 90% to 95% of the reference column

specimen’s capacity. This can be attributed to the strengthening of column specimens

using normal strength concrete as a jacketing material.

G2

-25

G2

-30

G2

-35

0

200

400

600

800

1000

1200

1400

1600

1800

225 256 289

Co

lum

n C

apac

ity

(KN

)



63


A B C C/A C/B


294.2

MC1 527.8 G2-25 1029.3 3.5 2.0

MC2 592.6 G2-30 1231.3 4.2 2.1

MC3 662.6 G2-35 1402.8 4.8 2.1

The ultimate load carrying capacity values of G2-25, G2-30 and G2-35 were plotted

together with that of UC and MC reference columns as shown in Figure ‎4-26.

It can be noticed that the application of Non-Fibrous UHPSCC jacket has provided a

high improvement in the compression performance of the jacketed column sections.


The obtained G2 ultimate load carrying capacity was greater than that obtained by

Mourad et al. ‎[25] who found that the jacket has enhanced the ultimate column

capacity by not more than 33% with respect to the control unjacketed column.

Adopting Non-Fibrous UHPSCC as a jacketing material has exerted lateral passive

confinement and worked with the column core in carrying extra loads before reaching

failure. That has given very improved sections in sustaining high axial compression

loads compared to the columns jacketed using traditional concrete.

Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 4.7.2.

Longitudinal Axial Strain

The axial strain values were recorded versus load values, the load-strain diagrams were

plotted for the three samples S1, S2 and S3 of G2-25, G2-30 and G2-35 jacketed



MC

1

MC

2

MC

3

UC

G2

-25

G2

-30

G2

-35

0

200

400

600

800

1000

1200

1400

1600

100 225 256 289

Co

lum

n C

apac

ity

(KN

)



64




0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G2-25-S1

G2-25-S2

G2-25-S3

0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G2-30-S1

G2-30-S2

G2-30-S3


65




0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G2-35-S1

G2-35-S2

G2-35-S3

0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain


66

Figure ‎4-33 shows that the average longitudinal axial strains of G2-25, G2-30 and G2-

35 have decreased obviously to about 0.0024 at failure points, lower than 0.0032 the

average axial strain of UC and MC reference columns at failures. The brittle behavior of

G2 jacketed column specimens can be alleviated by increasing the confining steel

stirrups in the jacket that will improve transverse encasement and so on the ductility.

Figure ‎4-33: Average Load-Strain Diagram of G2-25, G2-30 and G2-35.

Table ‎4-10 also presents the decrease in the longitudinal axial strains of G2-25, G2-30

and G2-35 at the rupture points with respect to UC and MC reference columns. The

measured G2 longitudinal axial strain was reduced to 0.74 and 0.72 times the axial

strains of UC and MC reference columns respectively.

Table ‎4-10: Decrease in G2 Maximum Longitudinal Axial Strain with Respect to UC and MC.

A B C


Failure

MC, Axial Strain

@ Failure

G2, Axial Strain

@ Failure

0.0032

MC1 0.0035 G2-25 0.0024 0.75 0.68

MC2 0.0032 G2-30 0.0023 0.71 0.71

MC3 0.0031 G2-35 0.0024 0.75 0.77

The G2-25, G2-30 and G2-35 axial strain curves were drawn together with UC and MC

curves as shown in Figure ‎4-34. The Figure ‎4-34 reveals that the load strain curves of

G2 jacketed column specimens are linear up to one third the ultimate load carrying

capacity but with steeper slopes than that of UC and MC axial strain curves, after that

the curves became nonlinear.

That means that the modulus of elasticity of G2 jacketed column specimens is much

higher than that of UC and MC reference columns. The G2 jacketed column specimens

reached their ultimate load carrying capacity at nearly axial strains of 0.0015 regardless

of their ultimate capacities, whereas UC and MC reference columns reached the

ultimate load carrying capacity at axial strains of about 0.002.

0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G2-25

G2-30

G2-35


67


It is worth mentioning that the brittle behavior of the G2 jacketed column specimens

can be attributed to the application of the Non-Fibrous UHPSCC mix as a jacketing

material. Unlike the results obtained by Ersoy et al. ‎[27] who concluded that the axial

strain of the jacketed columns was 0.002 at failure, this was attributed to the use of

normal strength concrete in jacketing.

Effect of Non-Fibrous UHPSCC Steel Reinforced Jacketing on G2 Failure 4.7.3.

Pattern

The failure mode of G2 jacketed column specimens was sudden. Cracks were observed

and formed approximately 30 mm from the top and bottom of the column specimens.

The Non-Fibrous UHPSCC jacket has burst loudly and crushed into several parts under

the pressure of the vertical compression load, showing no warning signs. The rupture of

steel stirrups was observed in the jacket steel reinforcement, and the buckling of the

longitudinal steel bars in concrete cores were also observed, see Figure ‎4-35.


0

200

400

600

800

1000

1200

1400

1600

0 0.0004 0.0008 0.0012 0.0016 0.002 0.0024 0.0028 0.0032 0.0036 0.004

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC1

MC2

MC3

G2-25

G2-30

G2-35


68



nine column cores strengthened by jacketing using Fibrous UHPSCC steel reinforced

jacket. Shear connectors were used to mechanically bond between column cores and its

jackets.

The results of G3 ultimate load carrying capacity were investigated in terms of jacket

thickness, and compared with the corresponding UC and MC reference columns. The

G3 longitudinal axial strains and failure patterns were obtained and compared with that

of UC and MC reference columns.

Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Ultimate Load 4.8.1.

Carrying Capacity

The several jacket thicknesses namely 25, 30 and 35 mm gave an obvious increase in

the ultimate load carrying capacity. The overall composite cross sections of G3 jacketed

column specimens were composed of two different concrete mixes; the column cores

were made of NSC mix and the outer jackets were made of by Fibrous UHPSCC mix.

Table ‎4-11 presents the average ultimate load carrying capacity of G3-25, G3-30 and

G3-35.



Area (cm2)

Jacket Area

(cm2)

Column Core

Area (cm2)

G3C1-S1 1141.9

225 125

All Specimens

have column cores

area of 100 cm2

G3C1-S2 1125.8

G3C1-S3 1155.8

Average 1141.2

G3C2-S1 1372.8

256 156 G3C2-S2 1322.5

G3C2-S3 1301.5

Average 1332.2

G3C3-S1 1596.5

289 189 G3C3-S2 1575.8

G3C3-S3 1650.7

Average 1607.7




several jacket thicknesses, almost similar to the obtained G1 and G2 results.


respectively while the corresponding ratios of ultimate load carrying capacity equaled

1.17 and 1.4 respectively. That has confirmed the almost direct proportional relation


specimens, same results obtained with respect to G1and G2 jacketed column specimens.


69

The results obtained also were in agreement with that obtained by Ramirez ‎[29] who

found that the jacket thicknesses are influencing the column compressive strength direct

proportional to the rate of the increase in jacketing area.


Table ‎4-12 reveals that G3-25, G3-30 and G3-35 jacketed column specimens have

gained huge increase in ultimate load carrying capacity 3.9, 4.5 and 5.5 times higher

than the UC reference column respectively. These results are in agreement with the

results obtained by Meda et al ‎[23] who concluded in his study that the jacketed

columns strength was higher 4 times the unjacketed one using the normal strength

concrete in jacketing.

The G3-25, G3-30 and G3-35 ultimate load carrying capacity was increased

significantly 2.2, 2.3 and 2.4 times higher than the corresponding MC reference

columns respectively.

Unlike the results obtained by Mourad et al. ‎[25] who found that the jacket has

enhanced the column carrying capacity by not more than 33% compared to the control

unjacketed columns.


A B C C/A C/B


294.2

MC1 527.8 G3-25 1141.2 3.9 2.2

MC2 592.6 G3-30 1332.2 4.5 2.3

MC3 662.6 G3-35 1607.7 5.5 2.4

The obtained G3 ultimate load carrying capacity values were plotted with the

corresponding UC and MC reference columns values as shown in Figure ‎4-37. The

application of Fibrous UHPSCC steel reinforced jacket provided a large increase and

improvement to the column carrying capacity.

G3

-25

G3

-30

G3

-35

0

200

400

600

800

1000

1200

1400

1600

1800

225 256 289

Co

lum

n C

apac

ity

(KN

)



70


Adopting Fibrous UHPSCC steel reinforced jacket has enhanced the lateral confinement

of the column specimens and thus increased the ability to sustain extra compression

loads. Whereas column specimens jacketed by wrapping fiber reinforced polymer (FRP)

as studied by Esfahani el al. ‎[12] have increased its column carrying capacity to about

2.0 times higher than that of the monolithically cast specimens.

Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Longitudinal 4.8.2.

Axial Strain

The axial strain values were recorded versus load values, the load-strain diagrams were

plotted for the three samples S1, S2 and S3 of G3-25, G3-30 and G3-35 jacketed




MC

1

MC

2

MC

3

UC

G3

-25

G3

-30

G3

-35

0

200

400

600

800

1000

1200

1400

1600

1800

100 225 256 289

Co

lum

n C

apac

ity

(KN

)


0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

nC

apac

ity

(KN

)

Axial Strain

G3-25-S1

G3-25-S2

G3-25-S3


71

Figure ‎4-39: Average Load-Strain Diagram of G3-25 Jacketed Column Specimens

Figure ‎4-40: Load-Strain Diagram of G3-30 Jacketed Column Specimens


0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G3-30-S1

G3-30-S2

G3-30-S3

0

200

400

600

800

1000

1200

1400

1600

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain


72

Figure ‎4-42: Load-Strain Diagram of G3-35 Jacketed Column Specimens


Figure ‎4-44 reveals that applying Fibrous UHPSCC jacket with reinforcement steel

cages in jacket has remarkably increased the longitudinal axial strain of G3-25, G3-30

and G3-35 jacketed column specimens to 0.0073, 0.0069 and 0.0083 at the rupture

points respectively.

Figure ‎4-44: Average Load-Strain Diagram of G3-25, G3-30 and G3-35.

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G3-35-S1

G3-35-S2

G3-35-S3

0

300

600

900

1200

1500

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

0

300

600

900

1200

1500

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

G3-25

G3-30

G3-35


73

Table ‎4-13 present that the longitudinal axial strains of G3-25, G3-30 and G3-35

jacketed column specimens were 2.28, 2.15 and 2.6 times higher than the axial strain of

UC reference column respectively.

Also the G3-25, G3-30 and G3-35 jacketed column specimens were 2.10, 2.15 and 2.68

times higher than the axial strain of corresponding MC reference columns respectively.

Table ‎4-13: Increase in G3 Maximum Longitudinal Axial Strain with Respect to UC and MC.

A B C


Failure

MC, Axial Strain

@ Failure

G3, Axial Strain

@ Failure

0.0032

MC1 0.0035 G3-25 0.0073 2.28 2.10

MC2 0.0032 G3-30 0.0069 2.15 2.15

MC3 0.0031 G3-35 0.0083 2.60 2.68

Figure ‎4-45 shows that the ductile behavior of G3 jacketed column specimens was

achieved strongly with respect to G1 and G2 jacketing styles. These results were almost

in agreement with that obtained by Meda et al. ‎[23] who found in his study that the

ductility was increased to about 100% the original tested columns.

It can be noticed from Figure ‎4-45 that the G3 jacketed column specimens reached the

ultimate load carrying capacity at axial strains of about 0.003, whereas UC and MC

reference columns reached the ultimate load carrying capacity at axial strains of about

0.002. This can be attributed to the application of the Fibrous UHPSCC steel reinforced

jacketing, which has highly improved the ductility performance of the G3 jacketed

column sections and increased the values of axial strains at ultimate load carrying

capacity.


0

200

400

600

800

1000

1200

1400

1600

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009 0.01

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC1

MC2

MC3

G3-25

G3-30

G3-35


74

It is worth mentioning that strengthening RC columns by applying traditional jacketing

material cannot increase significantly the column ductility as drawn by CAN ‎[24] who

found that the jacketed columns using traditional jacketing materials have gained the

same ductility of the monolithically cast reference columns.

Effect of Fibrous UHPSCC Steel Reinforced Jacketing on G3 Failure Pattern 4.8.3.

The failure of G3 jacketed column specimens was ductile. Cracks were observed after

loading up to 93% of the ultimate load carrying capacity. Warning signs were formed

on the external surface of the jacket before failure.

No rupturing for the transverse steel stirrups was observed. The high strength and high

ductility of the applied Fibrous UHPSCC steel reinforced jacket have protected the

concrete column core from crushing, see Figure ‎4-46. At the ultimate load, the jacket

bulged and bloated but still functioning as one unit. The bulging started at the first 70

mm from the top and bottom of the G3 jacketed column specimens, with continuous

hairline cracks surrounding the specimens.

When continuing loading beyond failure, the jacket showed wider cracks. Crushing

sounds was heard for the inner column core. Similar failure behavior was observed for

the different cross sectional area of G3 jacketed column specimens.


4.9. Ultimate Load Carrying Capacity and Axial Strain of G1, G2 and

G3 Columns with Respect to UC and MC

Strengthening column cores using UHPSCC jacketing by applying three jacketing styles

namely G1, G2 and G3 has improved significantly the column ultimate load carrying

capacity as observed in Figure ‎4-47 especially when comparing with the results of UC

and MC reference columns. The Figure ‎4-47 also shows that there was no significant

difference between the results of G1, G2 and G3 ultimate load carrying capacity. The

rate of increase in ultimate load carrying capacity was almost similar to the increase in

jacket thickness.


75

Figure ‎4-47: G1, G2 and G3 Ultimate Load Carrying Capacity with Respect to UC and MC.

The ultimate load carrying capacity of G1, G2 and G3 increased to about 4 and 2 times

higher than the corresponding UC and MC reference columns respectively.

Also, there was no significant difference between ultimate load carrying capacity of G2

and G1 jacketed column specimens. In spite of the absence of steel reinforcement cages

in G1 jacketed column specimens; Fibrous UHPSCC improved the characteristics of the

jacket. The Fibrous UHPSCC has exerted passive confinement on the column core to

sustain load several times higher than its ultimate load capacity.

It is worth mentioning that in spite of the absence of any surface treatment such as

scrapping, roughening or chemicals painting; the mechanical bonding using shear

connectors has shown good interface adherence between the old concrete and the

applied jacket.

Moreover, G1 jacketing style has proved a good bonding, even without adding

reinforcement steel cages in the jacket and that can be attributed to the application of L-

shape shear connectors along the four faces of the column cores.

It can also be mentioned that the addition of Forta-Ferro Polypropylene (FFP) fibers of

about 1.5% by the volume of UHPSCC mix has significantly improved the ductile

behavior and the compression performance of the jacketed column sections of G1 and

G3 as shown from Figure ‎4-48 to Figure ‎4-50. Noting that the failure modes of G1 and

G3 jacketed column specimens were improved giving warning signs before reaching

failure.

UC

MC

1

MC

2

MC

3

G1

-25

G1

-30

G1

-35

G2

-25

G2

-30

G2

-35

G3

-25

G3

-30

G3

-35

0

200

400

600

800

1000

1200

1400

1600

1800

100 225 256 289

Co

lum

n C

apac

ity

(KN

)



76

Figure ‎4-48: G1-25, G2-25 and G3-25 Longitudinal Axial Strain with Respect to UC and MC1.



0

200

400

600

800

1000

1200

1400

1600

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UCMC1G1-25G2-25G3-25

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC2

G1-30

G2-30

G3-30

0

200

400

600

800

1000

1200

1400

1600

1800

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008 0.009

Co

lum

n C

apac

ity

(KN

)

Axial Strain

UC

MC3

G1-35

G2-35

G3-35


77

Table ‎4-14 shows that the best ductility behavior was obtained by applying G3 jacketing

style. That can be attributed to the application of both Fibrous UHPSCC jacketing and

steel reinforcement in the columns jacket. However, the ductility improvement using G3

jacketing style was not significantly larger than that of G1 jacketing style.

As a matter of fact, the absence of FFP fibers in UHPSCC mix led to non-ductile failure

of G2 jacketed columns specimens. The jacket has crushed in loud voice showing no

warning signs in the case of using G2 jacketing style.

In spite of locating reinforcement steel cages in G2 jacketing style, the obtained axial

strains equaled about 0.75 the axial strain of UC and MC reference columns. This can

be attributed to the application of the Non-Fibrous UHPSCC which is a high

compressive strength material and accordingly very brittle material. The absence of FFP

fibers decreased significantly the axial strains of G2 jacketed column specimens.

Table ‎4-14: Summary of the Results for All Tested Column Specimens.

Column Notification / Pu (KN) / Axial Strain

UC MC G1 G2 G3

UC/294.2/0.0032

MC1/ 527.8/ 0.0035 G1-25/ 1056.3/ 0.0070 G2-25/ 1029.3/ 0.0024 G3-25/ 1141.2/ 0.0073

MC2/ 592.6/ 0.0032 G1-30/ 1231.2/ 0.0066 G2-30/ 1231.3/ 0.0023 G3-30/ 1332.2/ 0.0069

MC3/ 662.6/ 0.0031 G1-35/ 1520.9/ 0.0066 G2-35/ 1402.8/ 0.0024 G3-35/ 1607.7/ 0.0083

CHAPTER 5CONCLUSIONS & RECOMMENDATIONS

CHAPTER 5 CONCLUSIONS & RECOMMENDATIONS

79

5.1. Introduction

This research investigated the ultimate load carrying capacity and the longitudinal axial

strain of square RC columns strengthened by applying three jacketing styles. All

fabricated column specimens were subjected to monotonically low rate of uniaxial

compression loading.

Three jacketing styles namely G1, G2 and G3 have been studied experimentally to

investigate the effectiveness of every jacketing style. Fibrous UHPSCC was applied as a

jacketing material with G1 and G3 jacketing styles, whereas Non-Fibrous UHPSCC

jacket was applied with G2 jacketing style.

G1, G2 and G3 jacketing styles consisted of 27 column specimens in total (9 column

specimens for each jacketing style), while the UC and MC reference columns consisted

of 12 column specimens. All fabricated column specimens were tested at IUG Soil and

Materials laboratory. The results obtained in this research were summarized in the

following conclusion:

5.2. Conclusion

The following concluding remarks were drawn from the obtained experimental

observations:

Strengthening RC columns by applying Fibrous UHPSCC as a jacketing material

was effective and has reduced the total strengthened column sections.

The Fibrous UHPSCC can flow easily into narrow form sections without

segregation or honeycombing problems, even in cases of steel congested sections.

The relationships between the applied load and axial strain of the tested column

specimens were typical, a linear behavior up to one third of the ultimate load

carrying capacity followed by a non-linear behavior until failure.

The slope of the first part of the plotted load strain curves of UC and MC reference

columns was almost the same, while being steeper slope when strengthened with

Fibrous and Non Fibrous UHPSCC. Steeper slope means that the modulus of

elasticity of strengthened columns has increased.

Strengthening by applying Fibrous UHPSCC jacket increased significantly the

ultimate load carrying capacity and the longitudinal axial strain with respect to UC

and MC reference columns.

The ultimate load carrying capacity of G1, G2 and G3 jacketed column specimens

increased linearly having the same rate of the increase in jacketing area.


80

Applying several jacket thicknesses of 25, 30 and 35 mm with G1, G2 and G3

jacketing styles improved considerably the ultimate load carrying capacity in

almost a similar rate with respect to the rate of increase in jacketing area.

The G1-25, G1-30 and G1-35 gained significant increase in the ultimate load

carrying capacity higher 3.6, 4.2 and 5.2 times than the results of UC reference

column respectively, and higher about 2.0 times than the corresponding MC

reference columns.

The longitudinal axial strain of G1-25, G1-30 and G1-35 increased significantly to

about 2.1 times the axial strain of UC and MC reference columns.

The G2-25, G2-30 and G2-35 also gained significant increase in ultimate load

carrying capacity higher 3.5, 4.2, and 4.8 times than the UC reference column

respectively, and higher about 2.0 times than the MC reference columns.

The longitudinal axial strain of G2-25, G2-30 and G2-35 was reduced to about

0.74 times the axial strain of UC reference column, and about 0.73 times the MC

reference columns.

The G3-25, G3-30 and G3-35 also gained considerable increase in ultimate load

carrying capacity higher 3.9, 4.5, and 5.5 times than the UC reference column, and

higher about 2.3 times than the MC reference columns respectively.

The longitudinal axial strain of G3-25, G3-30 and G3-35 was increased to about

2.3 times the axial strain of UC and MC reference columns.

G2-25, G2-30 and G2-35 reached their maximum longitudinal axial strains of

about 0.0024 at failure, the severe reduction in axial strain was attributed to the

brittle behavior of the used jacketing material which is the Non-Fibrous UHPSCC.

Adding Forta-Ferro Polypropylene fibers (FFP) of 1.5 % by the volume of

UHPSCC mix has improved the properties by increasing the maximum

longitudinal axial strain of G1 and G3 jacketed column specimens to about 0.0067

and 0.0075 respectively.

The G3 jacketing style have significantly increased the ultimate load carrying

capacity and ductility of the jacketed column cores because of the application of

both Fibrous and steel reinforced UHPSCC jacket, however the increase was not

so significant with respect to the increase obtained by G1 jacketing style.

The failure modes of G1 and G3 jacketed column specimens were ductile giving

noticeable warning signs under loading before crushing and spalling out.


81

The failure modes of UC and MC reference columns were ductile giving

longitudinal axial strains of 0.0032 and 0.0033 respectively that was attributed to

the application of a normal strength concrete (NSC) in casting the reference

columns.

The failure mode of G2 jacketed column specimens was brittle. That was observed

by crushing loudly giving no previous warning signals.

5.3. Recommendations

The following findings and suggestions can be pointed out as recommendations for

future studies:

Findings 5.3.1.

As result of this study it is recommended to strengthen the four sides of square RC

columns using the Fibrous UHPSCC as a jacketing material, as it is a high compressive

strength material and reinforced by FFP fibers which enhanced the ductility and reduced

the jacketing thickness.

The self-compaction behavior of the Fibrous UHPSCC is very effective in casting the

RC column jackets easily without manual compaction. The importance of using self-

compacting concrete is the fact that the real life jacketing thickness is usually small and

steel congested which often causes segregation and honeycombing problems.

Suggestions 5.3.2.

The following point can be drawn for future studies:

Different bonding techniques should be investigated in further studies and

compared to what is obtained in this study.

Applying a localized strengthening jacket on different lengths of the strengthened

columns not only for the entire column length.

Studying the strengthening of columns after being loaded to actually represent the

columns condition in real life.

Studying the effect of the cycles of loading before strengthening the columns, as

well as the effect of eccentricity on jacketed columns.

Studying the behavior of slender strengthened columns under loading with

different slenderness ratios, and compare results with results of this research.

Studying the effect of the transverse steel stirrups.

Studying the efficiency of jacketing three or two sides of the RC columns instead

of jacketing its four sides.

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A

alternative, 21, 23, 32

appropriate, 37

approximately, 21, 79

average, 59, 60, 61, 62, 68, 75, 82

axial, 14, 21, 23, 24, 25, 31, 60, 63, 68, 75, 82, 91, 92,

93

B

batch, 46, 49, 55

behavior, 14, 24, 25, 26, 31, 34, 51, 91, 92, 93

bonding, 53, 54, 93

brittle, 14, 37, 92, 93

C

capacity, 16, 21, 23, 24, 32, 33, 34, 38, 60, 61, 62, 75,

91, 92

carbon, 24

characteristics, 34

Columns, I, 20, 21, 23, 25, 45, 67, 70, 75, 78, 81, 85,

86, 89, 95, 96

compacted, 49

competitive, 22

Composites, 95, 96

compressive, 14, 21, 23, 26, 35, 38, 59

Concrete, I, XII, 14, 25, 26, 34, 35, 95, 96, 97, 98

configuration, 25, 26

confined, 21, 25

connectors, 26, 33, 54

construction, 15, 20, 32, 97

conventional, 21, 40

D

damaged, 15, 20, 31, 59, 95

decisive, 20

demonstrated, 22, 33

devastating, 22

disadvantage, 23, 33

dowels, 54

ductile, 24, 92, 93

ductility, 14, 20, 21, 23, 24, 25, 33, 89, 92

E

eccentric, 21

effectiveness, II, 22, 25, 32, 34, 54, 91, 97

enhancement, 25

essential, 20

exhibited, 24

F

fiber, 24, 25, 37

Fiber, I, XII, 14, 38, 51, 96, 98

G

gauges, 57

H

height, XII, 26, 34, 93

honeycombing, 15

I

investigated, 24, 25, 31, 93

J

jacket, 16, 21, 25, 26, 27, 31, 32, 33, 34, 53, 61, 65,

66, 73, 74, 79, 80, 92, 93, 97

jacketing, 14, 15, 20, 25, 26, 31, 32, 49, 55, 73, 91, 93

L

longitudinal, 25, 33, 46, 79

M

mechanically, 49

monolithically, 31, 43, 61

monotonically, 57, 91

N

nonlinear, 91

O

original, 20, 21, 26, 27, 31, 33, 34

P

performance, 14, 15, 20, 25, 34, 35, 37

Performance, I, XII, 34, 95, 98

plotted, 91

Polypropylene, 38, 51, 53, 98

PPF, XII, 15, 20, 45, 51, 55

preliminary, 21, 40

R

Rectangularity, 26

reinforced, 14, 15, 95

reinforcement, 14, 21, 25, 26, 31, 33, 34, 46, 97

Repair, 20, 97

Restoration, 20

retrofitting, 14, 20, 21, 23

Retrofitting, 21, 25, 95

rupture, 14, 79

S

segregation, 15, 49

shell, 65, 73, 80

shotcrete, 33

significantly, 23, 24, 25, 31, 38, 86

spalling, 92

specimen, 24, 31, 32, 33, 57

specimens, 22, 24, 25, 26, 31, 32, 33, 40, 42, 48, 50,

56, 57, 79, 91

strain, 25, 27, 31, 38, 57, 60, 61, 63, 68, 75, 82, 92,

93

strapping, 21, 22

Strengthening, I, 14, 20, 32, 96, 97

T

technique, 20, 21, 22, 23, 33, 54

thicknesses, 44, 92

U

UHPSCC, XII, 15, 16, 20, 35, 38, 39, 45, 49, 51, 53,

55, 59, 65, 73, 79, 80, 91, 92

ultimate, 21, 25, 26, 27, 31, 60, 61, 62, 65, 66, 73, 80,

91, 92

unconfined, 21

uniaxial, 25, 31, 60, 61, 91

unjacketed, 60

utilizing, 20

W

Welded, 21

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